This is another Black Friday build - but the one I will standardize on for 2021

Overall, this is very similar to my existing Neutron-R builds, combining many of the budget components I discovered through my budget build adventures with a few high end components that I now consider to be worth the cost of entry because I'm progressing as a pilot.

The magic here is the flexibility on offer from running mid-KV 2207 motors on light frames. Anything from 1900KV to 2250KV allows for excellent performance on 4S, 5S, and 6S batteries (from 900-1500mAh), using a variety of Gemfan Hurrican props (51499, 51477, 51466, 51433)

Frame is a FPV Flight-Club Neutron-R. Same frame I've loved since the first one, I now own a dozen of these. The MaydayFPV designed canopy is simply amazing, and I snagged an all-red version just because I can.
Motors came from RDQ Clearance at less than $11 each. The XNova 1950KV 2207 motors in this case were too good a price to pass up, despite the somewhat dated-seeming c-clip architecture. The performance is all there, and the slightly lower KV (1950) in this case works fine. I originally wanted to slap a set of the gorgeous 533 motors on here, but the matching KV XNovas for half the price are hard to ignore.
Practically, substituting lower cost 2000-2350KV motors also works quite well, as there's always a way for me to fine a feel I like for racing between my battery options, prop options, and throttle limiting.
Stack is a Foxeer F722 with Aikon AK32PIN 20x20 V2. With sales, these were comically cheap, and F7 performance/convenience is impossible to beat at this price. I know that ESC is ready to party on 4S/5S/6S with minimal changes to settings via the firmware.
(I run everything at 48kHz PWM, 23° timing, 0.25 rampup power, and demag comp on low).
The overall tune is really straightforward, I have previously run BF4.3 with sliders at:
Master 0.9, PD Balance 1.3, P&D Gain 1.3, and FF 2.0, using DMinGain of 50 and DMinAdvance of 100. I am testing improved settings right now.
I try to disable gyro lowpass filtering and, run aggressive DTerm DLPF filtering (biquad at 1.4, dTermDLPF_Expo=10 - this is aggressive, not recommended), otherwise running the tuning notes suggestions for dynamic notch and enabling yaw LPF.
FPV Gear is just more of my favorites: Foxeer's PredatorV4 1.7mm was $20 from RDQ, and is a brilliant camera. I've given up and stopped running budget cameras, because I can reliably get such good performance out of cheap builds that it's worth paying extra to see where I'm going, otherwise I find myself constantly 'outrunning my headlights'.
The VTX is an AKK Race VTX, because $10 VTX does what I need it to. Finally, Foxeer Lollipop V3, again, on sale, but those are absolutely my favorite for ruggedness. The FC has a built-in VTX switch, making that entire thing easy.
Props are part of how I manage the very high KV - lower pitch is the answer. Gemfan 51433, HQ 5.1x3.6x3, and DAL T5040C props all work well on 6S setups. For 5S 1100mAh Black Series packs, this thing is a true animal. GF 51466 and TM5146 props are my favorite in that configuration. On 4S, I like the same 51466 props, and can use up my 51499 and DAL T5050C props as well.
Overall, the higher voltage lower pitch props give up a small amount of efficiency but return massive amounts of stability and performance in tight turns/moves providing much better lap to lap consistency. I find the sweet spot to be 5S on these motors as I can run them without any output limiting (cap transmitter at 94%, which allows the PID controller and mixer to still ask 100% power from a motor or two). On 6S, I limit to 82-86%, which is meaningfully more power on offer and probably contributes to the reduction in efficiency, but I am slightly faster and it feels more consistently locked in.
Batteries in this case are all CNHL units because price. The weight and performance of the black series is phenomenal, although I still use a lot of the older 100C G+ (White Series) packs because of insane value that I'm willing to punish them hard. Practially, the 5S 1100mAh packs are actually my favorite with this setup, running GF-51477's the overall pace is excellent with a light weight, and very little sacrificed at top end or full throttle because the XNova motors are so stout. I also have a couple Talon 5S 900mAh packs I picked up for cheap from CycloneFPV, for tighter courses that performance is wild, but I struggle to adapt to being able to pull 9G in turns and stay remotely accurate enough to be on the racing line.

Tune - Expect Betaflight 4.3 to include a Preset option with the exact tune I've tested on this setup. It will allow for anybody to run 4S, 5S, and 6S batteries using the profile auto-selection and have a tune that is able to aggressively track setpoint. This is unlikely to be the safest tune, but for performance at the limit is worth the tradeoffs, and the pace this thing is capable of on 6S unrestricted is absolutely nutty.

My best builds are not the planned builds,

This just reacted to sales, an turned into the setup I'm happiest to run.
I have probably spent too much money seeing just how cheaply I can build a good racing quadcopter, but can make the results consistently pretty good...
This partially breaks from that trend, because this is what I would build without any budget considerations. You can substitute frames (FlyFive33 SwitchbackPro Hybrid, Hyperlite F3LiX, or FPV FlightClub Neutron-R Hybrid StretchX are my favorite choices). Any other motor in the same size/KV range is going to perform brilliantly, and there are other ways to get the performance of this stack, but the Talon version is both the prettiest and best value in this case.
Running nicer RC/FPV electronics at your discretion is nice - I'd keep the antenna no matter what, and if you want to run Tracer/Ghost/eLRS/CRSF that's awesome, but my XM+ running D16 8ch still turns in 9ms framerates perfectly consistently. I know I can pick up 5ms of latency and have fewer dropped or duplicated packets straightaway by going to a 2.4GHz LoRa solution, but I'd rather turn the savings over my dozen Neutron-R quads on Rx into an entire spare quad of parts, which is what that cost difference turns out to be. I may change my opinion on this as my pace continues to improve, because the limitations of my RC system are very apparent in blackbox logs.
Short answer is that you'd be hard pressed to come up with a completey better build than this - some marginal gains that cost a fair bit are possible, but I'd rather have a matching fleet of these than something slightly nicer.
My all-in price of $183 is a black friday fluke, and required buying other stuff to hit minimum order quantities to ship free. This ignores the price of consumables (props, batteries), and doesn't cover spares.