RPL makes some good points. The tandem is a little heavier, awkward to handle and more expensive, but but every bit as much fun on the water IMO. Everyone's needs are different. I find it invaluable for those times the wife or kids want to go out and don't want to be left behind. It's also great or friends, pets and heavy loads (tons of space and capacity) for expeditions. In fact, I would describe it as the most versatile kayak if you're going to have just one.
The new '11 Oasis has dual steering, so you can solo from the rear cockpit (with ballast highly recommended)...

...or the front cockpit with half the ballast, or none at all:

Enormously popular for the community clean-ups as well!
