As others have mentioned, the play of others at the table has absolutely no effect on you - their mistakes are just as likely to help you as hurt you.
One exception - don’t play at the same table with card counters. Not only will they attract pit attention, but they tend to join the game when the deck is hot, and leave when it’s cold. That means on average you will wind up playing more hands with a bad deck and less hands with a good one. So the house has an even bigger than normal advantage over you.
If you’re not a card counter, it doesn’t matter where you sit. Pick a seat farthest away from the most obnoxious people at the table. For me, being a non-smoker, that means as far away from the smokers as possible.
For a card counter, 3rd base has a very tiny increased advantage, equal to seeing one extra round of cards per shoe, useful for playing strategy adjustments only. And since playing strategy adjustments make up only a tiny percentage of the overall gain for a counter, the overall gain to you is pretty trivial.
For a card counter, playing third base has one major disadvantage - the pit tends to watch the 3rd base players more carefully, especially in single-deck games where 3rd base actually translates into a pretty substantial gain for playing strategy variations. So it’s usually the LAST seat I will choose, since the biggest risk to my continued existance as a professional player is being booted out by the casino. It’s not worth the extra heat to gain an additional .02% advantage over the house.
There is an interesting strategy you can play in single deck if you are a card counter - it’s called ‘Depth Charging’. It involves playing all squares, but putting much bigger bets on the later squares than the earlier ones. The gains from strategy variation in the later hands more than overcomes the house edge on the earlier ones, and you can make an overall profit without having to scale your bets up and down. Unfortunately, the casinos tend to be on to that little trick now, and a depth-charger will find himself barred pretty quickly if he’s playing for significant stakes.