Depends on the type of plane. If it's an MD-80, you'll have two seats on one side of the aisle and three on the other, so you might want to try to get an entire row. If it's a 737 or 757 (or most other planes), it's a three and three configuration. Regardless, I'd vote for front of the plane too, but only for the easy on, easy off feature. The back certainly is noiser on an MD-80, which has the engines in the back, but not necessarily on other planes with the engines under the wings.
All have restrooms in the rear, but the 757 also has restrooms in the middle of the main cabin. If that's what you're on, try to get in the forward section so you have the best of both worlds.
Also, try seatguru.com