Try out loads.....I kept off gels for a couple of years as I focused on ultras but have gone back to them in the last few months for speed endurance training and marathons (burning carbs at a slightly faster pace)
I can't get on at all with SiS. They are isotonic so quickly absorbed and can be taken without water which is good, but as a result they are lower in energy. For me, though it's the high fructose content - causes almost immediate stomach cramps. After lots of experimenting I now use Gu - no fructose, high energy but thick so must be taken with water.
As has been said you may be OK with jelly beans/babies but could also try chocolate, flapjacks, shotbloks, any of the other gels on the market (torq, lucozade, Tailwind etc).
Main thing without doubt is to try various things out to see what works and what doesn't, and how much you need - that's what your training runs are for. I can do a marathon on empty, but I know a guy that has a gel every 20 mins (he's a much better runner than me). You may also want to think about electrolyte replacement as well, either capsules (SCap or Endurolite) or dissolvable tablets you lob in your water bottle (Nuun for example).
