Three can do a pretty good job. I was happy with three for a long time...I've just started wanting to do some of the shard instances and other high level stuff and it can be hard to find a group for some characters so I will make my own.

As for the dungeon/group areas, pretty much everyone is fine until you get into the newer/higher level ones. The only time that boxing can be difficult in instances is when you have to click stuff or do certain things for a boss, but there's not many of those type of places until you get into the newer and higher level areas.