SF as it's one of the most solid fighting game franchises available. Of these three choices, Tekken is the most awkward choice available since it's a 3D fighter while the other two are very, very famous and popular 2D fighters. Now that isn't saying that Tekken isn't well known but it's definitely not played as much internationally in comparison to SF or MvC.
I don't play 3D fighters, so Tekken was an obvious boot out of the poll, but MvC and SF are very solid games, each with a strong and extremely large competitive scene supporting them. Comparing the two series, SF is a more fundamental-heavy game (i.e. footsies, zoning, etc) whereas MvC is an extremely rush-down heavy game, comprised of a large amount of bug exploits at a high level of play. That doesn't mean that there fundamental game strategy and play doesn't apply, but it shines more heavily in SF, especially with ST and the recent SF4 series. That being said, SF allows for a whole variety of play styles and pretty much gives you some of the best basics that you can carry over to other 2D fighters.