Fappy said:
I prefer between 3 and 4. Any group over 5 is too big in my experience. I was a player in a game with 9 people once... worst game of DnD in my entire life.
9? Yikes.
Although, if we're speaking of worst experiences... I once ran a game. At one point, I had 21 people who wanted to play in it. So I split the game in half - I took 10, and I appointed another GM from the players to take another 10. I gave him instructions about what he needed to do so that we could (eventually) bring both groups back to the main plot.
Not only did he not follow those instructions, he went entirely off on his own, so that the other group had no idea what was going on. I was too busy trying to juggle 10 players. In the end, the whole game was a massive mess. Terrible, terrible experience.