Of the variety of "power", "energy", "health" bars (such as Cliff and Luna 
bars), which is the most powerful, energetic, or healthy? Or to phrase 
differently, what are each ones advantages and disadvantages?

The answer depends on which nutrition theory you subscribe to.

The main point of difference between different types of nutrition bars is their 
carbohydrate/protein/fat ratio.

The official opinion on the recommended ratio is embodied in the USDA Food 
Guide Pyramid, which recommends consuming 2 to 3 times more carbohydrate-rich 
foods than protein-rich foods, and limited consumption of fats. See 
http://www.usda.gov/cnpp/pyramid2.htm.

The Food Pyramid has generated a heated controversy, which is well represented 
on this site:
Low Carb Research
http://www.lowcarb.ca/

See, for example, this article:

http://www.lowcarb.ca/articlesb/article337.html
The USDA Food Pyramid is wrong

Another good review of the controversy is available on the WebMD site.

One recent article is located at:
http://my.webmd.com/content/article/1728.50484
Get Ready: Controversy Likely to Heat Up About Long-Term, High-Protein Diets.
Latest Findings Suggest Higher-Fat, Lower-Carb Diets Improve Insulin Resistance 
Sensitivity.
By Jane Schwanke

Other related articles can be found at:
http://my.webmd.com/related_results/1/25/article/1728.50484

Research advocating higher animal fat and protein consumption is presented at 
the Weston A. Price Foundation site: 
http://westonaprice.org/

See, in particular:
http://westonaprice.org/myths_truths/myths_truths_nutrition.html


Once you make up your mind on which carbohydrate/protein/fat ratio is best for 
you (taking into account your health conditions), you have to decide what you 
think about vitamin and mineral supplements (are you getting enough from food? 
do you need higher than average doses of certain vitamins and minerals?).

There are RDA's (Recommended Daily Allowances) for most vitamins, described at 
the USDA Food and Nutrition Center site:
http://www.nal.usda.gov/fnic/etext/000105.html

However, they are controversial as well; see, for example:
http://www.nutritionfarm.com/your_health/articles/rda_story.htm
http://www.drlam.com/supplements/intro.cfm

Finally, after you decide which nutrition theory you subscribe to,
you may want to check out nutrition bar comparison tables at these sites:
Willner Chemists
http://www.willner.com/BarsMain.htm

Endurance World (a sports website)
http://www.angelfire.com/electronic/ultramentor/bars.html


Here are some helpful Google searches:
"energy bar nutrition comparison"
"carbohydrate protein fat controversy"
"RDA controversy OR critique"