I've had a couple of good matches that I felt were something of a challenge, but eventually I notice their weaknesses and they don't perform well after I start to counter them. It also helps that I main MK, too. But I'll also pick Lucario, Pit and Zelda at times.
I saw this one decent player who played more than one character. But his pikachu was pretty pro at spamming thunderbolt. I mean he'd be sneaky about it. He'd do the thing where you'd be on a platform above him and he'd down b and nail you out of nowhere. He'd do it while you were chasing an item or fighting someone else, so your focus wouldn't be on him and he'd catch you off guard. He didn't miss either, and since you never saw it coming you wouldn't even try to dodge.
But his melee game was weak, and once you realized that he was just gonna down b you while hiding below it became very easy to predict and move out of the way. I think he started to get flustered when I started to avoid his moves, and he offered little resistance when I confronted him in close combat.
There were other "okay" players. But I haven't met someone so pro that he left me in awe or anything. If anything I'll be happy to find one other decent player in the match that I can have some fun with.