As far as noise goes, it depends on the plane and where the engines are mounted. The far front, though, is usually a safe bet for a quiet spot.
As far as convenience goes, that depends on the individual airlines and how they board the planes. TED, in their infinitie wisdom (at least the last three times I've flown them and United), has adopted a policy of boarding the front of the plane first. This is completely rediculous, because then they've got the aisles blocked and the people in back can't even get into the plane to get to their seats until everyone loads their giant carry-on suitcases into the overheads and gets all of their kids into their seats. I'm not 100% sure what all the other airlines are doing. The one certain thing, though, is that you will get off the plane first if you're in front (unless, of course, it's a heavy with two jetways, which is usually only on transcon or intl flights).
As far as safety goes, it doesn't matter. Every plane crash is different. There is no way to be able to say in advance what the safest place to be for any particular accident would be. So, my advice is to relax knowing that the odds of ever being in a plane crash are about as good as being struck by lightning with a winning lottery ticket in your pocket. MUCH more important than picking a specific seat, is knowing the location of the exits near you (there is a reason the flight attendants say that, because it's true) and KEEPING that seat belt fastened when the sign is on and ANYTIME you're in your seat.
Cheers,
MG