Mike makes a great point that I agree with about not sitting at first base because you don't have as much time to think about your initial decision (to hit, stand, split or double).
Lots of players will give the player at THIRD BASE lots of grief, dirty looks and snide remarks about things like taking the dealers bust card or messing up the flow of the cards EVEN WHEN YOU ARE PLAYING CORRECT BASIC STRATEGY. Of course, you shouldn't let these players get to ya. I was surprised to see this happen often. Seems lots of players think they know BJ but they really don't.
I like to sit in the middle (anywhere between first base and third base). It gives me a little extra time and you don't have to listen to people's complaints. Just know though that if you are next to third base and that player leaves, you BECOME the new third base.
I hope this helps.
And, by the way, I would say sit together...it's more fun.