I'll add my reasoning for E-Gel, check out their comparisons against others:
link
-Complex Carbs with dual carb source - research shows this is the best combo
-Low sugar - less sold on this one, but yes I'd agree it's likely true from a blood glucose standpoint
-Much Higher electrolyte content than competition - close to ACSM recommendation of 500mg Sodium and 200mg Potassium per 34 oz water (remember every 2 g carb needs 1 oz water, no matter what your source)
-No artificial sweeteners
-Isotonic solution - means rapid absorption, but I'd argue this is true of any product as long as you meet the 2g carb to 1 oz water
-Antioxidants - helps with muscle soreness, but probably not beneficial until post run
-Rapid Mix - only relevant to E-Fuel, but personally I find it mixes "ok". Better than Hammer, but worse than Powerbar. However after consuming 34 servings of 8 oz I tend to get grumpy.
-Gluten free and no artificial color, flavor or sweeteners - personally this doesn't sway me, but to some it might matter
Pro/Con - At 37g per package it can be seen as a good thing and bad thing. Less packages per serving, but to some consuming 37 g carbs (or 18.5 oz water) is a bit much. Granted the 18.5 oz water just needs to be consumed between packages, but that can still be a lot of water for some.