Dennis...over the years, I've tried most of the leading brands of energy gels. Some people favor one brand over another, but I have fairly equal success with gu, power gel, hammer gel, carb boom, etc. Some of the gel flavors are just not tolerable, so taste tends to weigh heavily in my choices. I think most people just have to try various brands and flavors to see what they can swallow, and what sits well on the stomach. Your flavor choices are greatly reduced if you want only those without caffeine. I know that gu flavors without caffeine are the banana blitz and strawberry-banana. WIth power gels, I think the tropical, plain, and vanilla flavors are without caffeine. I have found that I can tolerate most of them just fine without stomach issues as long as I don't mix them with any type of energy drink. That means water only a few minutes before taking a gel, with the gel, and a few minutes after the gel. So, if you are using sports drinks like gatorade, powerade, etc, space it around the gels. I tend to use electrolyte tablets such as S Caps, Endurolytes, or Lava Salts and shy away from the sports drinks for that reason. The same holds true for other energy products such as clif bloks, sports beans, performance bars, etc. I simply don't use anything but water to wash them down. When I forget that rule is when I start having stomach issues. For those long runs where intensity is not as high, I have also had good success with perpetuem, which is a Hammer product that comes in powder form and is mixed with water. I've used gels in conjunction with the perpetuem without stomach issues. Good luck experimenting.