With the PS3 tech demo, and AC, the Cloud model has been given a bit of a facelift. So at this point we've seen 5 different versions of Cloud:
FFVII: World mode - the low poly club-fisted Cloud
FFVII: Battle mode - more detailed but still a fairly low poly Could
KH: PS2 version of Cloud, maintains the look and feel of the FVII but with greater detail
PS3 Tech Demo: I call this one the "Crazy-eyed Cloud", but looks more 'realistic', and looses the cartoony feel.
AC: The most 'human' Cloud.
My personal favorite was the KH model. Very nicely detailed version of Cloud but still maintained the same look and feel of the original 'battle mode' Cloud. The PS3 version and the AC version, seem to have lost the whole personality of the character, IMO.
Anyway, what do you think, which is your favorite version of Cloud?