Rayovac indestructible or energizer hardcase are good candidates. Cost efficient, decent runtimes, two modes, 2xAA.
Funny enough the reason I bought a new light for grandpa was because he said his broke after just a few uses. I was at his house this past week and he brought out the broken one. It was one of these Energizers. I tinkered with it and started by bending out the contact in the tailcap a bit to make sure that it was pressing firmly on the battery. Sure enough, that fixed it! Once it worked again and I got to play with it, I agree this is actually a really good flashlight for an older person.