There are all kinds of nutrition bars available, from energy bars, to protein bars, to weight control, to gluten free, to breakfast bars, and the list goes on. Unfortunately, many of these supposed "nutrition" bars are really just glorified candy bars.
What to look for when selecting a nutrition bar:
Sugar - Look at the nutrition label and see how many grams of sugar there are per serving. . .and does a full bar equal 1 serving? Select a bar with 5 grams or less sugar per bar.
Fiber - Don't rely on fortified bars to meet daily fiber needs. Isolated fibers, such as inulin, chicory extract, and oligosaccharides do not necessarily provide the same benefit as foods naturally rich in fiber. Select a bar that provides ~3 grams of fiber. Ideally this fiber will come from whole grains, dried fruit, and/or nuts included in the bar.
Vitamins and Minerals - Don't use a nutrition bar to try and meet 100% of the recommended dietary allowance (RDA) for vitamins and minerals. Look at the food label and see if it's providing 100% of the RDA. There are potential side effects from consuming too much of certain vitamins and minerals. Select nutrition bars that do not provide 100% of the RDA for vitamins and minerals.
Calories - How many calories you want in your nutrition bar, depends on how you plan to use it. Is it to be a snack between meals or is it to be the meal? As a meal replacement bar you'll want at least 250 calories per bar. If it's a between meal snack, find a bar with 100-150 calories per bar.
Bars have their place, but they should in no way be used to replace a healthy, well balanced diet of fruits, vegetables, whole grains, lean protein, and heart healthy fats.
Keep in mind too that all these bars are highly processed. You can't go out to a field and "pick" a nutrition bar off a vine. There is a lot of manufacturing involved in the production of a nutrition bar. Read ingredients labels thoroughly and make sure you really want to be consuming some of the additives and preservatives necessary to make these products shelf stable.
Maybe a banana with a handful of nuts would be just as quick to grab and healthier in the long run.
Have you been struggling to make heart healthy diet changes? If so, access the report "How to Make Heart Healthy Changes into Lifelong Habits" at http://hearthealthmadeeasy.com.