For those of you worried if SSB4 for 3DS will pull a Brawl on us regarding the online portion of the game... well, it kinda does, but only if you have a lousy ISP (sorry Ners). According to Youtuber Maximillian Dood, it all depends on various factors, like Upload Speed, Amount of players, Items, and so on...
Some users have reported that they've had between 70 and 80% of success rate when playing online, best of all is that distance doesn't seem to play a big part on the quality of the connection.
VadePrimer, a member of Smashboards, posted:
I have about a 70% success rate with online battles. 2 player only is more likely to succeed but I've had pretty good luck with 4 player with items on and very little lag. Since I live in america, and I'm playing mostly people from Japan online, I feel that is a fair success rate. I must say that normally I have a 90% success rate with most any other online games (Fighters, Online RPG's and FPS) so being that this isn't a wired connection on an underpowered 3ds playing a pretty intensive game I feel 70% is solid. I hope it reaches 80% range when it is released in America.
It is known that Nintendo is constantly monitoring the input by users and all the data it can collect to provide support and patches to make the online experience a pleasant one, but it is waiting for the game to release in American and European territories to gauge how good or bad the situation is.