As far as shooters go, I'd say timing is fairly important especially if you're doing something like sniping.
There really shouldn't be a problem with Smash Bros online. It'll be just like any other game online, if you can find a good server, you'll find a good game. If you find a crap lag server, you'll find a crap game. That's my experience with fighters online DOA4 is a game where (depending if you can counter or not) timing can be critical as well, but it doesn't seem to be too big of a deal. If anything lag tends to give you a defensive advantage if everyone is lagging at the same rate, you get a little more reaction time if you see things coming.