i think you're on drugs

gotta be futari for my money
interesting to see how different people have different ideas of what is and isn't tough though.
from what i've played, i'd put the non-looping games in this order:
mushi original > deathsmiles (no canyon+low rank) > espgaluda > mushi maniac > esprade > futari original > guwange > futari maniac > ibara > dangun feveron > espgaluda 2 > mushi ultra > futari ultra
something like pink sweets is very difficult to place. and i think a 2-ALL on ddp, ketsui, progear, or doj, would be as tough as the ultra clears. the ketsui and doj 2-ALLs probably between a mushi ultra, and futari ultra
oxstu had a very interesting list from arcadia readers, over at shmups, that is well worth checking out