Quest Rewards do not all vendor for the same.

There are a number of addons that will give you the vendor value, or you could look it up on wowhead.com or whatever site you prefer. I use the one that comes with auctioneer.

The general rules are
2h weapons
1h weapons
Wands
Plate
Chest
Pants
Shoulders

Mail chest will vendor for more the plate boots. Staffs always seem to vendor for the most. Wands will sometimes sell for more then 1h weapons.