I'm not a big fan of the gels, mainly because when I'm on the bike the stuff seems to end up everywhere: my chin, hands, handlebars... (same with my fluid replacement drinks). Plus, if there's no trash can handy there's no way to get rid of a sticky, used gel packet without shoving it back in your back pocket. I like the shot blocks a lot because they're easy to pop in and not messy at all... You can also adjust your caloric intake by the number of blocks you injest (each one is about 33 calories). Several of the flavors also come caffeinated. The only downside is they can stick to your teeth (like gummy bears) and you have to wash it down with something.

For my fluids, I have taken a liking to MotorTabs. They are tablets that dissolve in water, so you can keep extra tabs handy. They taste like (not so sweet) fruit punch and best of all, if they spill on me there is no stickiness involved.