The main differences between a 6 and 9 player table is the action.
If you are a tight player then 9 is better for you. Wait it out till it gets down to 6-7 players (SnG) than change gears when you start getting decent hands to see the flop. On a cash table, it allows you to sit back and watch the play to get a better read on who's doing what.
A 6 person table allows you to play more hands and be more aggressive.
Those pocket pairs are usually not going to go up against a better pocket pair.
The profit on a 9 player SnG is better than a 6 player.
Ring games of 6 usually mean you will see many different players at the table. They bust out and leave, so getting a read maybe a little more difficult.