A lot of things are different. Jet Pack, gauntlets, cape and especially color, scratches & battle damage. Generally speaking, ESB gauntlets, jet pack and body armor are the same basic bluish green color. On Pre-Production suits, the right gauntlet is a reddish brown, the left is a dark yellow. On ROTJ, both gauntlets are red. The construction of the left gauntlet details are different on each version as well.
The
shape of the body armor is basically the same throughout all three versions with some differences in the location and size of the dents, dings and scratches.
I would suggest searching for threads here on the differences. Also you may want to buy one of Brak's Boba Fett reference Cd's. It's money well spent.
If you want a basic Boba Fett costume that is easily recognizable for a Halloween party or something like that, all the details may not matter that much to you. If you want to get into the 501st Legion, then it matters more.
The best advice I was given was to choose a version
YOU like and then learn about that one and build
that version. After all, you are the one it matters to most.
Good luck, post pix and keep on trying.