Apart from the Uratama, the other Japanese Connections are the Tamagotchi Plus, Keitai, Keitai Akai, Entama, and Familitchi. The Japanese Tamagotchi Plus is identical to the Connection V1 in all respects except for language, and that your character will become sick every now and then for no particular reason. For this reason, I prefer the English V1, which only gets sick if Hunger or Happiness metres empty. It's also my understanding that the Familitchi & Royal Familitchi are analogous to the V5 & V5.5 respectively.
The Keitai and Keitai Akai have no English equivalent, and so they are unique. These releases are quite simple - three games, and a gotchi point system to buy items from the visiting shopkeeper. As with the Tamagotchi Plus, characters will randomly become sick, which is a problem if you cannot tend to your Tamagotchi all day. The Akai is certainly interesting with its red pixels and red-themed characters - the screen is a little hard to see, but it's quite a fascinating release nonetheless, and something I would recommend to all collectors.
The Entama play style is very similar to the Uratama, except with different characters & games. A nice version to have (oh, the beautiful shell designs!), if you don't mind something functionally similar to your Uratama.
I haven't mentioned the Hanerutchis, Odenkun or Tamasukus also from the Connection era. They're all different from the 'traditional' Connections, and there are lots of guides & videos available showcasing them. My other advice would be to research the games on each release you are interested in, as some of them (esp. on the keitais) are rather difficult if you cannot understand Japanese. Hope this helps
