If you ask me about STU I think hands down a 2.8l BMW E36,E46,E92 it really won't matter much. That is what I wanted to build if someone would just by the fastest ITA Neon in the country (shameless plug )

In STL I like the 240 sx with the SR20,or the BMW E30 1.8l is, maybe a BMW Z3 would be a good fit as well?