HI Aries,
Largely its about heat transfer area. The more heat transfer area you have, the quicker your recovery will be. Personally, I would opt for the longer ones. Not only will the longer ones most likely have more heat transfer area, their length will help the water "draft" or pull the colder water from bottom as it rises from being heated (i.e. turning over the water in your tank). This works much in the same way a longer chimney drafts better than a short one.
In either case, adding a small circulation pump on the tank side will greatly improve recovery time....if you feel this is a must. Personally, I hate the idea of added initial cost and Kwh to run it (even though it is tiny).
Cando