I have tried all three.
GU tastes the best and is usually the cheapest(~$20 for a box of 24 on sale).
Clif is just meh...I don't like their gels.
Hammer seems to have the biggest effect on me and they taste pretty good(but not as good as the GU flavors), but they are expensive($1.35 for a gel), unless you get the jug which is $20(I just got one in chocolate flavor).

Favorite flavors (best to worst):
GU: Espresso, Just Plain, Chocolate
Clif: I hate all the one I have tried
Hammer: Chocolate/Espresso(tie), Montana Huckleberry

I think it all matters on the consumer's preferences....I hate all fruit flavored gels.(Montana Huckleberry is the only fruit flavor that tastes good to me)

For electrolyte supplement I use GU Brew, it is cheaper than most others and it works great for me!

For solid food, I prefer Clif bars, pretty much all the flavors taste great and they are usually a dollar each at Trader Joes.
I like the Hammer bars more, but they are wayyy too expensive! I bar is over $2!!! I can't afford to use them regularly, but I do pick the up sometimes when they are on sale.

I also use Clif Blocs sometimes, but I prefer gels....
Honey Stinger jellies taste amazing, but are pretty expensive.
I usually get Power Bar Gel Blasts from Target when they are on sale($4-5 for a 4 pack). They taste REALLY good and the seem to work pretty good, energy delivery is almost as fast as gels.

Sometime if I go on a really long ride(80+ miles) I take a nutella sandwich with me. Mmmmm...nutella...

Hope this helps!!