I started with the Nitto NT05, which is a 200TW tire and they came in sizes that I wanted. Unfortunately, they really suck for autocross. I found they wore quick and didn't grip very well. Moral of the story, don't get those if you're looking for lots of grip.
Last summer I switched the to the Faulken Azenis RT660s. I went with 275-35-18 in the back and 235-40-18 in the front. These tires are light years ahead of the Nittos. The tires were new when I arrived at Moparty. I did 25 autocross laps, and at least a dozen speed stop laps. The "Falken" embossed in the center tread was still visible after all that. I will likely get my front wheel widened so I can run 275 squared.
To put the grip difference in prospective, when I autocross I start in 2nd gear so I don't have to shift. With the Nittos, I could blaze the tires to rev limiter if I wanted to when starting. With the Falkens, the car just goes.
I chose the 660s for the following reasons, listed in prioritized order:
1.) They are consistently rated as one of the best 200TW tires (top 3 of many tests)
2.) Sizing that works for my car
3.) Price and availability
Some other 200TW tires I considered:
Nankang (hard to get sometimes)
Bridgestone RE71RS (heard they wear quick)
Dunlop Direzza ZIII (old design but I've driven a Miata with them on track and they were pretty good)
Falken RT615 (cheapest)
Yokahama Advan A052 (most expensive, but really good)
Nexen N Fera Sport R
Hancook Ventus R-S4
Hope this helps. Happy shopping!