Generally there are two types of Labrador. The quiet, amiable, laid back ones (probably not so much from working stock, or partly from such stock) and the working ones who are lean, mean, working machines. And those in between, of course. I've had both. My present dog is full of energy, is hard to handle when I go shooting, but is a great worker. He doesn't, for example like sitting at a peg. Much prefer to be picking up or in the beating line, hunting. A previous one was really laid back. Loved sitting at the peg and was happy if he got the odd simple retrieve at the end of a drive.
So the thing to do is, if possible, see both parents and see what their temperaments are like. But of course it's a Labrador, so if it's a part time working dog that's also a pet, don't worry. All of them will make perfect pets, be endlessly patient with children and be as loyal and affectionate as anything. As for which one in the litter you pick, remember that they will only be a few weeks old and their characters will not be fully developed. I'd say not to go for the most forward one, nor the most backward. Look for a middle of the litter one that is alert though and, not unimportant, just the one you like the look of. Good luck.