Aside from having different characters, there are a few key differences:
v1:
can connect to v1 - v4.5
only has 2 games all it's life (jump and dance)
only has 2 food items
does not have gotchipoints or store or codes
only gets a total of 3 items: Ball and 2 adult gifts (changes with character)
random chance of games or gifts in connections
has no tamatown
v2:
can connect to v1 - v4.5
has 4 games, 1 gained at each evolution stage (jump, bump, heading, and slot)
earns gotchipoints and has a store and codes
has multiple buyable food items
has multipe buyable toy items
can choose gift or game
can give items of your choice as gifts
has no tamatown
v3:
has small, round antenna
can connect with v1 - v4.5
has 6 games (notes, bump, heading, flag, and sprint)
earns gotchipoints and has a store and codes
has multiple free and buyable food items
has multiple buyable toy items
can choose gift, game, or visit.
can give chosen items as gifts
has v3 tamatown
v4/v4.5:
has antenna with a ball or star on top
can connect with v1 - v4.5
has 5 games (jumprope, mimic, shape, dance, and flag)
earns gotchipoints and has store and codes
has multiple free and buyable food items
has multiple buyable toy items
has mail and school and jobs
can give chosen gifts
has v4 tamatown
v5:
has antenna with a face and roof
has multiple characters raised at one time
can connect with other v5s only
has 4 games (tv surfing, tea time, golf put and shoe pairs)
has tv channels (shopping channel, which is the store, dating channel, which is the matchmaker, and travel show, which replaced pause)
can earn gotchipoints
has multiple buyable food items
has multiple buyable toy items
has the v5 tama and earth expo (basically tamatown)
If something doesn't make sense, PM me and I'll explain