I have personally kept 3, 4, 5, and 6 in a community tank. And of all those, i found that 6 worked the best, with very little bickering in the beggining and absoultely none later on. 5 was pretty much the same, except it took them longer to settle down, 4 and 3 did not work very well at all. It resulted in torn fins, shy fish who would not eat, and alot of bickering.