Personally, I like tables with 6-7 people at them. I HATE full-ring games with 10 people, especially when plaing limit. If you pick up a big hand (such as KK or AA) and do what you are supposed to do...RAISE, you still get called by multiple hands. This is NOT what you want to happen. With a huge hand like AA or KK you want to play it heads up or against at the most 2 opponents. WIth so many players at a full-ring game, you are bound to get called with hands like 34 suited and they hit a two-pair, straight, flush, etc.
If you are a loose player, full ring games are more beneficial because you can call a lot of preflop bets and be in large multi-way pots, which is what you want if you like to raise with lets say 22 in first position.
The table selection is mostly based on what your personal preference is. If you like playing in big pots between 5 players...play 10-seat tables, and if you like to play heads-up or against 2 opponents (usually) play the 6 max games...