2-circuit
I think if you like the looks of the new gen 3, then that's what I would go for. If you have money to purchase it, then be prepared to spend a little more to have it customized if it needs it by someone that specializes in throttle stop carbs for the Super classes.
As part of my hobby of racing, I have been building engines, rear ends and carbs for years to support my cash flow needs for the racing. I buy good used brand name carbs, rebuild, do minor upgrades and then find racers who want them over new carbs because of price.
I have had about every brand of customized carb and a bunch of throttle stop carbs. It seems the throttle stop carbs all have a common theme, intermediate circuit leaning or elimination. I assume this is to accommodate the time on the stop and coming off the stop. They all seem to work great as bracket race carbs too. There may be more than just changing the intermediate air jet to make a good throttle stop carb.
I prefer to get 3 circuit carbs and then lean out the intermediate circuit, and perhaps have to richen the main jetting. 3 circuits also seem to have better resale value as most people don't realize a 3 circuit can be rich on the fuel curve.
In your case, the 2 circuit may be a good choice for throttle stop racing as mentioned in an above post by someone who knows a lot more than I do on this subject.
If you want to see the most exotic throttle stop carb, look on DaVinci's site at the SPIDER 1050 and 1250. He completely eliminated the intermediate circuit and them added HARLEY motorcycle custom jet pods above the main boosters to bring in the new intermediate circuit after the main circuit was already in, above 5000 RPM. It has jets in the pods to tune it for the throttle stop. I had one and it worked great. But it had external fuel hoses that I was a little uneasy about. Not sure if he makes them anymore. And they were $1895 new.