I think that nutrition bars are good as supplemental meals or snacks...but not that they will necessarily increase your mass, strength, etc.  Some are marketed as such, but that's just because they pack the various supplements into that FORM to take.

The best bars for snack substitutes or even meal replacements (better eat 1 1/2 or 2 though) are the ZONE PERFECT bars.  They have more protein in them than almost any other bar I've found (like, 3-5 times as much) and they taste like candy bars.  They are well balanced on fat, calories, and protein.  Best of all, they are one of the cheapest to buy as well...about $1 each.

If you need to load on carbs, then I would suggest buying a supplement like Weight Gainer or something and make the shakes.  Whey or Soy protein made into shakes is good too...I prefer to stack the protein more than the carbs because I am not trying to "Get Big" just endurance strength.

Just my humble non-expert opinions.

I enjoy a bar now and again. However I have found that if you have the time to make the shake equivalent it is much cheaper. Especially if you are going for the protine.

Hard to do if you don't have a blender at work...

I like the Met-Rx Protein Plus bars Costco sells

You can premix them or buy the shaker bottles with the grate to help with actually mixing them.... assuming you got a fridge.

Balance bars are actually quite good, both taste wise and based on amount of protein etc. But Zone bars are about as good as they get in that price range, especiall if you go to a place like Costco and buy them in bulk.

I've noticed some people will buy nutritional bars without realizing what the hell they're buying. I have a female friend who's always on some sort of diet (she likes to combine three or four different diets at the same time, but only the bad parts of them). She bought a bunch of PowerBars mistakenly thinking that they would be better for her than the Snickers bars or whatever it is she usually likes to snack on.

For those who might not know, PowerBars are high carb to give you an added energy boost while working out. They're not intended as meal replacements or snacks. If you're just hungry and need something to snack on a PowerBar will only add more carbs to your body, carbs that won't be used for anything. Instead they're more likely going to be stored as fat.

Usually between 14g and 16g.  I don't ever recall seeing the Balance bars with that much protein...either that, or they were real high in carbs or just simply cost too much compared to Zone Perfect.

Skullworks brings up a good point in saying that a lot of the "power" type bars are mainly carb loaders for working out.   The Zone Perfect seem to be a good all-around balanced snack.  Find which one tastes the best for you in your budget and go with it!

I went to Costco today and picked up a box of Carb Solutions. 60g bar with 25g of protein. 250 calories but only 14g of carb (none from sugar).
Taste pretty good too.

The box of Balance bars I have here in the office are 6g fat, 22g carb, 14gr protein per bar.  

I second the Carb Solution Bars... I've been munching 2 to 3 of them daily for over a year now... the best tasting is the 'Creamy Chocolate Peanut Butter'.  24g of protein, 14 carbs, 240 calories.  If you do some shopping around, you can find them for $1.05 to $1.33 each.