When looking at what the bars contain, there are (as in all food) three main sources of energy: fat, carbohydrates and protein.
The two bars linked have similar composition when it comes to this, so unless you are really measuring your other intake during the day, the difference is negligible.
If looking at bars more in general, there are a few differences to look for, depending on why you want to eat the bar:
- "Energy bar": Usually quite rich in carbohydrates, advertised for eating before/during workouts.
- "Recovery bar": These have a bit more protein in them, usually good post-workout (especially as a quick source of protein after strength training)
- "Fitness bar": More or less meant to make you less hungry in as few calories as possible. More for weight-loss than actual fitness.