I have been using GU energy gels for racing for about 2 years now. During a race, I prefer the salted watermelon flavour, as it is not too harsh mid race.
GU is thicker than most brands, but I actually prefer that. This particular flavour has 450mg of amino acids, 125m of sodium and 20mg of caffeine per serving. I found them great for summer races/training when sweating a lot. The amino acids and sodium really do make a difference. The caffeine is an added bonus. I would normally alternate 1 non-caffeinated GU to 1 caffeinated GU for longer races, and this approach seemed to work well.
There are a ton of options on the market for racing and training fuel, but I feel like GU covers what you need during a race, and keeps it very simple. I will continue to use this brand as I train for the Boston Marathon and my first Ironman 70.3.