AllStars isn't a bad game, but it's not something I can sit down and play for hours. Younger players will probably enjoy the game a bit more, but I feel that it's pretty constricted, and the whole concept of gaining power to get kills(however fresh it may be) is broken and I find myself joining games and losing because everyone is either throwing me or sapping my power with items.
On the note of Console VS Vita, they are almost identical. I bought the CrossBuy version and the only difference is some menu options on the vita that support touch screen and what not. The two games can actually cross play with each other which is why I have both copies, and the only thing I notice is a very slight latency with the connection, which could very well be strictly internet, or fixed with a patch.
In my opinion a lot of the characters are broken and the stages feel small and constricting. I don't like the fact that you have to build up your energy by hitting someone when each attack does something different. I also don't like that the stages throw elements of other games in the background, that can often times have nothing to do with any of the characters on screen. I like the concept but the backgrounds are always the same for each map so it's kind of lackluster.
The combat is fluid on both versions and the characters are all fun to use. The only problem is some have attacks that are far stronger than others, and super moves will often times go in a direction I don't want them to. You end up having to adjust your shot prior to using it and this broadcasts your intentions far too much.