Technically speaking, they're all vers but Richard, Chester, Harold, & Darius seem more top aligned
Spencer and Dwayne are more bottom aligned.
I agree with the statement that all of the characters are pretty much versatile. If I had to give a list left to right from "prefers bottom" to "prefers top", I'd probably arrange it like this after having played through each route as they are so far:
Dwayne, Spencer, Harold, Chester, Darius, Richard/Dozer
This list doesn't really seem accurate, though, as none of the characters are strictly one or the other and land more in the middle:
TL;DR: All of the characters seem pretty versatile and enjoy it either way lol