Space Marines, Space Wolves, and any other army CAN be tournament competitive. I know that may sound cheesy or idealistic, but it really is true, you can find examples of literally every codex that has placed highly at a major tournament recently. It all depends on HOW you play them. And you will only learn how to play an army well by, well, playing a lot.
Furthermore, allies are allowed in 6th edition. So if you think Space Wolves are cool, and Ultramarines are cool, you could always paint up a few of each and use them together.
Basically I think you should just start out by reading some codexes, and finding some units that you think sound cool, and then trying to make them work. There's really not a better shortcut than that.
I guess if you want an army that hangs back and shoots a bit, I would give the edge to Space Wolves, just because they have one unit, Long Fangs, that is particularly good at doing just that. But honestly, you could make a totally shooty Marines army, or a Space Wolves army that has no long range shooting at all, and probably do pretty well with either one if you played it well.
Anyway, good luck! It's a very fun game, partially BECAUSE it is so wide open like this.