Battery life, build quality, ability to hold zero, waterproof to X depth, materials used, and overall reliability. What's the difference between a Glock and a Hi-Point? I will say that a Strikeforce is fine for most people though...
Aimpoint says they will run strong for 3 years off the same battery... if the s ever hits the fan you are not going to have a whole lot of access to batteries
I have mixed emotions about both of them. I own both and one of the lesser expensive Trijicon's. I agree with joshua, that there may come a time when you're not going to find batteries. My two favorite rifles are different configuration plain jane AR-15's with open sights.
I initially bought a cheaper red dot and it was adequate, but found a good deal on an Aimpoint a few months later. There is a difference in quality. The glass is clearer, the dot sharper, and overall just seems tighter/better built. I am well into the second year of battery life on mine.
Aimpoints last through explosions and hold zero better than the mounts. They're virtually paralax free and last 3-7years on one battery depending on the model. Aimpoint makes the best red dot sight on the market. I've heard Eotech is good too but their battery life sucks compared to Aimpoint and I don't have much time on one myself. For a red dot on a potential fighting rifle why get anything else? You should always have irons as a back up though. Aimpoints are expensive so if the rifle is just for fun and it means putting food on the table then the Primary Arms or Vortex red dots should be fine.
Cheaper optics are fine for plinking around. With Aimpoint and Eotech, your really paying for those extra features. Battery life is one, although i've never gotten a T1's battery to last longer that a year, that is 1 year of continious on. The beaten you are able to give them and the warranty/service that backs them up.
Trijicon Acog is also a good example. Costs a small fortune but warrentied for life in most cases. And the warranty is transferable if i'm not mistaken.