Well, it's different for everyone; it depends on what you like about Tamagotchis. If you get bored easily and have to constantly be doing exciting things, then the newer versions are better. If you enjoy the simplicity of caring for a single, adorable digital pet, then the older versions are better.
I like ancestor Tamas alot because they live for a long time, because they can't breed. A healthy little Tamagotchi P1/P2 should live to be at least 17 years old. A perfect little Mametchi usually lives to be 22.
Now, they
do get needy in their old age. After age 16, they start needing care every 5-10 minutes. But, this only lasts for several days, and then he goes on home.
I like newer Tamas such as the Tamagotchi Connections and Tamagotch Plus series because they have been improved. They have new features, better sounds, and adorable new characters. I like the Japanese Tamas better (EnTama is my fave); Connections are becoming too focused on designs and complicated features...
I think newer Tamas are
slightly better, but old ones are awesome too!
-DDDTrooper