I used to think same as most but, In the last two years its been proven that ether setup can win at the highest level. The only class I have not seen it(lay-down seat) win (yet) is in TAG. I’ve seen “sit-up” karts with lay down seats run identical lap times as a regular “4cycle chassis” and vice versa.
The true question is, which seat compliments your physical size, and you driving preference I think. period.