I like both. I don't think one is "better" than the other. They're both simply the same at heart, with a few changes in characters, games, and jobs. They have the same amount of features, so you can't exactly judge them on that, and they're similar features with slight changes besides.
The big differences, as mentioned before:
-characters. A huge difference here.
-games. Also a huge difference...in terms of "better", there isn't real
-jobs. Not so much.
Characters...
The V4, in my words, has more...subdued characters. It has the classics; Mametchi, Memetchi, and Kuchipatchi, along with others like Maidtchi, Shimashimatchi, and Makiko, for example. The V4.5 is circled around the Ura characters. Some characters have "Ura" versions of themselves, and others are completely new characters. Observe:
V4 character (Pyonkitchi? I forget xD)
V4.5 character (I don't even remember anymore -.-)
Also, a note: the V4.5 does have a few originals (If I'm correct, Mametchi, Memetchi...and Mimitchi or Kuchipatchi, 3 of those 4), but only as Universals.
Games:
As mentioned by GotchiGuardian, the V4 comes with 5 built in games: Jump Rope, Mimic, Shape, Dance, and Flag. Note that you don't unlock these all at once. The V4.5 also comes with 5 games: Climb, Tug Of War, Apple, Shapes, and Manhole. Neither of them have the same games. In my opinion, the V4.5 games are a bit shorter than the V4, but both are just as fun.
Jobs:
This doesn't really have too much difference. Some jobs are the same, some are different. I can't really go into detail...there's too many to remember. xP
Okay, I hope I didn't make your brain explode with all this info.