I don't think there's a best really. I had to pick my favourite, that's more likely what it's gonna come down to anyways. I'll just stick to giving my opinions on 3 games instead.
For a competetive fighting game experience, I would say street fighter. This is because it's popular and easy to get into, but with enough complexity and balance for it to remain a competetive fighting game. Sure, it's a lot easier to defend yourself now (focus attacks, reversals) and there are some bouts of imbalance (yun and fei long come to mind currently), but honestly, no fighting game is perfect, and street fighter has a nice aesthetic and doesn't go heavily into the anime artstyle that most extremely competetive fighters have. It's a great game for the western playerbase as well as the eastern one (of course). This is the one I voted for.
SSB is probably the best casual fighter out there. You can't really say that it's not a fighter. It has the core rule that every fighting game has, which is to fight the opponent. They had to greatly sacrifice balancing, and the game definately has core problems with its design that causes major imbalance (in ALL of the games, the main one would be attack priorities), in competetive play, but that doesn't matter in casual play anyways, because they play what they want, these imbalances don't matter in low level play.
MK I definately think is worth mentioning too, it's definately good for what it does, providing visceral play. I think it's worth a mention because I think that's the only thing it's got going for it. Sorry, it's just a poorly designed fighter. I mean, UMK3 was a high point (IMO), and then the creators of MK just made crap over and over again. The only community within the game was online. MK9 has tried very hard to change that. They did make a lot of changes, pretty much all of them for the better, but I personally think it only barely made it to be a competetive game. At least when it first came out that was the case. There have been several patches to fix the gameplay, but will it be enough? Or will the game sink back to having a online only community again?
The other fighting games have their merits, I don't feel like giving my opinion on them though, I think I have said too much already. However I don't think there really is a best game, because certain people want certain things in fighting games.
However I think games that strive for competetive gameplay (especially offline tournaments) inherently have an advantage over other fighters, save for ones that give party elements. This is because there is the option for serious play AND competetive play.