Oh, definitley the V5. It's much easier to care for if you have a busy schedule or want to do other things than care for your tama.
For example, if you leave it alone for a few hours it will only have a few messes and a few empty hearts. The bonding percent thing isn't that much of a deal, it's actually pretty easy. And, you don't have to worry about weight! You can feed your tamas when their hearts are empty and won't have to play any games to lose the weight 'cause that's not a problem on the V5. There are also tons of new characters and different families you can raise and there is a plethera of items you can get! There's also a TV icon, that includes the TV Shop (the Shop), Dating Show (or Matchmaker, so you won't have to worry about missing the Matchmaking times), and Travel Show (the pause feature).
The only cons are you can't donate to the Tama King and you can only connect to other V5s. That's about it, as far as I can think of.
I think you should get the V5.