I look for:
1. VARIETY!!! I cannot eat the same energy bar twice in a row. Bleck!!!
2. CALORIES - it's gotta be high in calories
3. Flavor - it has to appeal to me or I'm not going to eat it
4. Carbs mostly, but also protein and fat
5. Minerals and vitamins and stuff like that
6. Price - no way am I going to fork over anything more than $2 per bar. I'll buy a bag of oatmeal cookies instead
A suggestion: go to your local grocery store or pharmacy ... buy one each of all the energy bars that appeal to you and meet your requirements. Try them. You'll decide which ones YOU like that way.
Personally, I like Peak bars, Powerbars are pretty good, especially the new Harvest ones, and I hate Clif bars. But there are also about 30 other brands out there, some are good, some are not.