What's the best X-men vs marvel vs street fighter vs capcom vs snk???

Sorry to post in general, but the games are on Saturn, PSX, and Dreamcast, so couldn't decide which forum to pick.

I was wondering which from this series are the best to have? (assuming you just want a couple to best represent the whole series, rather than getting them all).

First on the Saturn there was:

- X-Men: Children Of The Atom

And then came:

- Marvel Super Heroes

And then they started mixing them up:

- X-Men vs Street Fighter

- Marvel Super Hereos vs Street Fighter

And then the series continued on the Dreamcast:

- Marvel Vs. Capcom

- Marvel Vs. Capcom 2

- Capcom Vs. SNK

- Capcom Vs. SNK 2

Now, X-Men is unique in that it has all the x-men characters. All of the marvel ones only had a few, and they all follow the same minor-tweak progression from MSH through MvC2.

So right now I have X-Men COTA and MvC2. It seems like this would be a good representation of the whole series. But I'm just curious if anyone things there's something worthwhile in the middle of that.

I don't have the Capcom Vs. SNKs. I've read that it doesn't really work mixing the two different characters with two different fighting engines. To fill in the SNK blank in that list, I have Dream Match 99' (KOF98), which is supposed to be a Dreamcast favorite (of 98 through 2002). I also have the Fatal Fury anthology.

And then there's the rest of the streetfighter collection. I have Alpha 3, which kind of gives everything of the alpha series. I've never been thrilled with anything in the Street Fighter II series.

Anything you think it worth adding to the collection?