It depends on what you want , Rainydaysxo.
v3 - The 'core' of virtual pets. You feed them , train them , mate them , etc. The animations are fairly cute , and the characters will make you smile. They need quite a lot of attention & will keep you busy.
v4/v4.5- Now you can get jobs , mail , go to school , and have skill points =D I don't reccomend this for school-use , since it requires more attention than any other version. The characters are adorable and the games are pretty fun.
v5- This tama doesn't need to much attention , ( unless you choose to give it some ). Now you don't have jobs , mail , or skill points ... but you do have 3 characters in one , new characters , games , and the screen is bigger. You can have bonding and the C button animation does more than any other.
So it's really your choice , if you need more information , feel free to PM me.
//Ms.MilkMalty