For gels I first go to Hammer, then Clif Blocks, then Clif shots 9In likeability). I tried GU and it really doesn't agree with me. With Hammer gels, you can only find them in specialty/bike stores (in my experience), but for some reason, when I take them, I feel like I get an extra kick and they are easy on the stomach. Clif blocks are good because they are a little more palatable and not as messy.
For energy bars, I go with Clif bars and Promax. Clif bars are good, but they usually land me straight to bathroom, so I only eat them pre-race. Sorry to be so honest, but were all friend here, right?
I just started eating Promax and they taste realllly good. Also Clif bar now makes Clif Rocks and they are bite sized bar pieces and have this coating like a M&M. They are great because you can regulate how much you want at what time.
And while on subject, eating too much of gels/bars, no matter how good they taste, can really wreak havoc on your system. Pay attention to the caloric content as well as, how many calories you are expending during activity.