In comparison to how I normally play, I'd say I'm pretty terrible with my mains in Wi-Fi. Though I guess in the entire lag-afflicted spectrum, I'm pretty good nonetheless. But yeah, with Marth, it really sucks, because you could perfect all his skills in normal play, but then have practically nothing to show when you get to Wi-Fi, which is why I gave up using him, or anyone, really, in particular. I'd say lag is always unavoidable, which is a shame, because it Brawl would be such an awesome game if the online was better (mainly in regards to lag, but there are some other aspects they could improve a lot, too).