This for the PS3, though, it depends on your internet connection. The better the connection, the better the online. It's all a matter of the range of Wi-Fi accessibility.
Usually, within a certain radius, no matter how strong your connection is, the system will eventually cut the connection.
Wii - ||/||||
PS3 - |||/||||
XBOX360 - ||||/|||||
Those are based on the lengths by five lines. Each line would represent how good the range is, or how far it would go. I've played all three and my cousin owns all three. The Wii was made for mainly "Family Play", so, consequently, the online sucks. The PS3 was meant for graphics, blue-ray, and gaming, but not too much online except for maybe DLC and some co-op, i.e. Little Big Planet. The XBOX360, on the other hand, was not only made for the multi-player, but an awesome online as well.
Depends on what you're looking for. If it's graphics and good games, PS3. If it's good games and epic online, XBOX360, (assuming) you already have a Wii, if you don't, then get it if you want sucky online, poor graphics, and a chance to play GameCube games that are better than most current Wii Games.