I think it really depends on what kind of owner you're like.
If you like the feeling of having a tamagotchi as a single pet then I say stick with the old tamagotchis. The new V5 is really for people who like the idea of raising more than one tamagotchi, and like to have their tamagotchis change often. I find this keeps things interesting, but at the same time you can never have enough to time to get attached to a particular character/characters before they get married and have new tama babies.