It really depends on your approach to the game. If you are looking to improve, daily correspondence offers you the chance to really study positions, check the databases and learn something about openings.
On the other hand, if you play a lot of games, getting your head back into the position can be difficult.
Which is generally better to learn? Too often I feel like I lose track of what I was trying to accomplish with my position from one day to the next in Daily games, and it seems like faster-paced chess is generally more popular. Do you all find that timed games generally help you learn and improve better than dailies?