This is my template for my 2019 racing setup, relying on using Hybrid Floss (5" front, 6" rear) frames on 6S-Ready setups. The Formula:

6S Ready Electronics /\ 2207 Motors /\ PredatorV3 Cam /\ LED Bling

The frame is a hybrid (5" front, 6" rear) Floss - in either Floss 2.1 or Floss3.0 configuration.
Serge now offers this setup out of the box for Floss 3.0 kits, but I cobbled this together on my own since I planned on using the Brain3D and PHX-3D Nylon Canopies with these builds.

The concept is that with reverse prop direction, this setup allows for the maximum amount of undisturbed air to reach the rear props, which in tight negative angle of attack maneuvers (like split-S, corkscrew, and hairpins) minimizes the need to react to propwash caused by rear propellers being in dirty air.

I happened into testing out this setup when I broke an arm at a race and only had a 6" boomerang to throw on the back. After one heat on that setup, that's been my go-to frame layout since September of '18. If this setup is good enough for Evan Turner to dominate at MGP Nationals, it's more than adequate for me. Curiously, this comes in at the same weight (within 2g depending on motors) as Evan's, and these motors are range between around 1750-1900KV, making this a really close clone - which I didn't realize until two weeks after I took my first pair of 2019 race season builds out for a maiden the week of MultiGP Nationals.

I'm still partial to running DAL T5046C props for racing, although these feel absolutely amazing on Gemfan 5149's and Gemfan 5146.6 props. I happen to have quite a few sets of the MCK props in pink, so I primarily fly those on the pink SunnySky Edge Racing 1800KV motors, while the XILO 2250KV motors tend to run the 5149-3 props on 4S and 5S, but I'll move to lower pitch HQ 5.1x3.6x3 props on 6S. Race days, I still find myself leaning on the V2 Cyclones when it counts.

For aesthetics, I've been really enjoying the PyroRace LEDs on the bottom, with a 5V LED backlighting the canopy. The overall simplicity afforded by running racewire setups is great, and the backlit nylon canopies look great at an overall minimal weight penalty. The real advantage to me is the antenna mounting becomes very simple and durable, otherwise it's a ~20g weight penalty overall.
The pictures here don't do it justice for how good these look with any of those propellers in any kind of lighting - or how striking the LED setup is in low light conditions.

"I can't guarantee that I'll fly well at a race, but I know I'll at least look good crashing"

The flight control stack is the PyroF4/Furling with the PyroF4 V2.1 Pit PinI/O switch to turn off video. Paired with a Unify HV Pro, and Foxeer Lollipop, that's a pretty impressive do-all setup. I've also gotten tired with cobbling together odd RC Receiver setups, so this has the R-XSR also VHB taped to the back side of the PyroF4 board.

For capacitors, I've added either the big honking 35V 1000uF capacitor on there, or a pair of 470uF caps, so this is pretty solid all around.
I probably need to make the leap to CRSF before I collect too many more FrSky receivers, but even my setups running FlySky X6B's are competitively fast.
I have poor luck with VTX setups - the Unify HV Pro Race is what I've tried to settle on, but I've killed a few of those, and I've just started running Eachine VTX03's with a pit switch on 5V and had honestly excellent luck (power-on interference isn't the best, but the integral pit switch prevents the biggest problem with those $8 transmitters, and that's heat soak while disarmed).

My preferred software setup is Betaflight 4.0 - primarily because I've found that the D-Min capability on D-Term allows me to achieve great propwash performance while maintaining cool motors and better efficiency, particularly when running 6S on higher KV setups (2000KV, 2150KV, 2250KV, 5S on 2500KV). Beyond that, the only other changes worth discussing are rates (for me fairly low RC rates with roughly stock super rates resulting in ~500°/s Roll/Pitch and ~275°/s Yaw, a filters which really matter the most. I still run fairly minimal changes from default on filters - drop the Gyro LPF 2, bump the gyro LPF1 up to 150Hz, and allow the D-Term filter to drop down to 125Hz. While the net gain in phase latency is pretty minimal, this setup with D-Min values around 12-16, I've been able to finish heats on delaminated arms and annihilated props.
One key for me is managing throttle through limiting maximum throttle - even when running 4S on 2000KV motors, I limit throttle to 95% input. I still see 100% motor commands in blackbox recordings, so the added resolution is always a good thing, and at peak throttle the FC can only use the PID sum that allows stable flight that is capped by the one motor at 100% throttle, so adding resolution on the stick is great. On the more aggressive 6S setups, I will limit motor outputs or RC throttle stick outputs down into the 65-75% range depending on props.

I have nine builds following this template now, each with some minor variation of motors. As far as impressions on each:

• The BrotherHobby R6 Motor versions are the smoothest I have, with the lowest noise floor on blackbox logs I've ever seen. Outright power isn't the highest, but the 2207 1750KV setup is very light for the power delivered. For aesthetic reasons, these are my favorite.
• The T-Motor F60 ProII are the most powerful smooth motors I have, although the ~1850 actual KV of the motors helps with raw power at a pretty low efficiency cost. Still my overall highest performance rig, despite older RC/VTX hardware.
• The SunnySky Edge Racing 2207 1800KV motors are beastly powerhouse motors, putting out just ridiculous amounts of thrust. They're heavy, but I'll take that for the price and outright thrust they offer.
• The XILO 2250KV 2207 POPO pro motors excel as multipurpose motors, since they excel at 4S and 5S, but be capable of going stupid fast on 6S. It's a fairly light motor for a 2207 size, restrict me to running POPO props, although I already adore the Gemfan 5149's and DAL 5249's.
• The iFlight TachyonV2 Rainbow motors are actually 2208 motors (stated 2207), and weigh so much they'd need to be. Really similar levels of crazy thrust to the Sunnysky motors, but they weight an additional 4g each. I like the rainbow look, but will choose the Xing or SunnyskyER line over these.
• The RCX LS2207 is another excellent budget motor, with great performance for cost, but the bearings they come with aren't that good. Sounds silly complaining about quality on $9 motors, but I'd happily pay $15 for a variant of that motor running quality 4x9x4mm bearings and a more aggressive bell for grabbing props.
• The EMAX ECO 1900KV motors are another really impressive budget performer, with actually remarkable power on offer. Not quite as much thrust as the nominally lower KV SunnySky or T-Motor options, but these are surprisingly powerful for the weight. Importantly, they're $12, and my current favorite low-cost motor... I just happen to prefer the slightly heavier and more powerful SunnySky for the same efficiency at net $6 upcharge on a built quad
• The BrotherHobby R6 2500KV version for 4S builds is also an exceptional performer, and is a surprisingly efficient setup all said and done. I'm still outlasting people on their efficient 6S rigs running year-old CNHL 4S 1300mAh packs on this setup. Both the T5046C and MCK GF51466 props are exceptionally good on this setup.

On a budget I recommmend the EMAX Eco 2207 1900KV ($12), or my personal preference, SunnySky Edge Racing 2207's if you can find them <$15/motor ($13.49),
If you're after performance which exceeds my piloting skills, I feel that it's worth the extra scratch to run R6 or F60 motors.

Batteries don't have to break the bank either, when you find a good sale on CNHL, Turnigy Graphene, Pyrodrone, Pulse, Tattu, or GNB packs you'll be in great shape. For 4S, the venerable CNHL 1300mAh 100C packs are impossible to beat for the price, although the 1500mAh Ministars are impressive. 5S 1300mAh-1800mAh anything works great, and on 6S the whole range of 1000-1500mAh work great.

I've found that there are two setups for racing quads I really prefer - either very lightweight nimble setups which rely on low AUW for handling performance, or these more powerful setups that take advantage of tall stators and big batteries for power and stability.
For going really light weight, those setups actually perform best with 4S 1000mAh-1300mAh batteries anyway (<400g AUW builds on 2205 ~2600KV motors with light props), going to 6S only feels great if running >150second races. Dry weight on those quads in the 205-225g range is generally best to maintain durability and flight time, though up to 245g still works quite well.

For me personally on most tracks, the optimum setup of choice is these bigger beasts running 6S packs, which brings the dry weight of ~315g up around 500-525g depending on batteries. With the props/motors I prefer, there isn't a drastic performance difference between the lightest 6S 1000mAh packs or the heavier 1300mAh packs I own, and helpfully the performance isn't differentiated that much by battery quality either - just about any decent 6S pack will perform super-well, so just get the cheapest good batteries you can (usually on-sale CNHL packs)

I still recommend building a 6" frame with 2150KV 2207/2208 motors

The flexibility afforded by building that way allows for 4S/5S/6S performance, 5"/5.1"/5.2"/5.5"/6" props, and lets you standardize to one quad setup that offers for cruising, long range, efficiency, or outright speed.
If you can standardize all the parts to this setup, you'll find yourself money ahead, and can justify running higher quality parts because you need fewer spares.