I love all the connections, and even if the simplicity of the v1, v2 and v3 is nice, I also love the concept of skill points, family types and jobs of the v4 and v4,5.
The v1 and v2 are a bit more of a challenge than the v3, in my opinion, as the games are slightly more difficult making it harder to keep the tamas happy and their weight down. This goes especially for the v1, where the only two games are really challenging, and the neediness of the characters is above average.
Also, if you're thinking v1, either get two, or get a v2 along with it as connecting is the only way to obtain items on it.
The v2 and the v3 has loads of awesome characters, with the v1 characters being more basic and not as surprising. I don't find the v4's characters quite as special and exciting as the earlier connection ones, but all are still super cute and everything so it's all taste.
The v4 and the v4,5 have reliable systems for getting almost all the characters you want, except for the universals that appear at random as a result of bad care.
As a contrast the v2 and v3 has not really any growth charts that are 100% reliable.
The v4,5 ura set of characters are a nice change from the usual ones, even though I can't say which is best.
All are awesome, so I don't think you'll get dissappointed.