I've used both. I like the way the amphipod fits, but I have a bad shoulder, and I find it difficult to reach behind myself and pull it out. Unfortunately, it is not an ambidextrous design. I also find I don't have enough room for an inhaler, gel, and some money.
The fuel belt I have does not have a pocket, but I have added one that is sufficient for the items I mentioned. In addition, I like some fuel on the run, but more water, so I can fill some bottles with water, others with accelerade, and have my pick. I also run with a dog, so he has one bottle designated as his. The design of the belt is more comfortable than it may first appear.