What size? 250, 210, 150. The ideal setup for the best racing drones is different.
Before we can advise on setup, YOU need to make this decision. Also, what I find works well for me, could be to overpowered for you depending on your skill level.
The Best Racing Drones
What I would recommend is, buy an RTF racer from a known company like a storm, lumpier, TBS, for example. These are with designs to be fast enough to learn on, fast enough to be competitive at lower skill classes, durable sufficient to handle most crashes, and not that much more expensive than sourcing all the parts yourself.
Once you are ready to step up to the next level, then you can upgrade the motors and escs. Just do your research, find engines around the same size maybe a little bigger, with more power and higher VK, and you should be good to go. Don’t like/broken the frame for some reason? Buy a different structure and swap the electronics over
If you have your heart set on building a racer, I’m not going to tell you brands to buy, But I will give you an idea on where to start for a 210–250 size for a beginner.
Motors: 2205 outrunner with 2100kv or more, capable of 300+W of power. Some people will say this is to fast for a beginner, but I beg to differ. This is what I am using to teach my 13 y/o son to fly. The extra power enables you to hover easier and get yourself out of a belly slap situation easier.
ESC’s: will depend on the motor, but give yourself a 10% headroom. If the motor specs say 12A max amp draw, run a 15A ESC. This helps the system not to be overloaded and last longer. If using OPTO ESC’s, you will need a 5V BEC to power the flight control and receiver.
More Beginner Drones
Flight Control: I’m biased in my choice here, anything that runs an open-source firmware. For a beginner, I recommend one with stabilization that can be on/off as needed, but when your skills increase, a dedicated race board is a way to go.
PROPS: LOTS of them!! I fly pretty hard, near many different obstacles. Depending on the brand/makeup of the accessory, I can go through 10–12 in a day between my son and myself. Buy BULK packs, 40+ props at a time. You WILL use them. Oh, and for the size, 5-inch diameter, 3–4.5-inch pitch, this will be written 5030–5045, I find three-blade props suit me the best, so get a few different configurations (2,3,4 blade) and see what you like best.
Lipos: 1500mAh-2200mAh at least 75C discharge. Larger mAh in the pack gives longer flight time, at the sacrifice of weight. Larger C rating gives more sustained output amperage, Not much more to say here.
Radio Gear: 6 Ch minimum if you want to use stabilization or have different flight modes. Get the best you can afford, and it will last you longer and probably allow you to bind more models at the one time.