I like San Andreas over Vice City, just because the map is so much bigger and more varied. Plus the 2 player spots are great fun
Me and my friend used to spend hours playing 2 player mode, my friend would usually drive the bike and I'd sit on the back and be the gunner, made police chases a lot more interesting since I could shoot out their tires, gas tanks and drivers pretty well. You could also auto target cars and helicopters which made things interesting. Or the other thing that was fun was having duels between us
2 player mode quickly replaced single player turns as the preferred play style.
As for cheating in Morrowind, that is probably one of the most fun games to cheat in. Especially if you used the editing tools to make insanely enchanted items. I loved giving myself 250 jump, 10000 archery and tonnes of Mana and just going around wiping out ton after town like some sort of unstoppable ninja.
Fallout was another game that was great for replay, and also a lot of fun to cheat in once you beat it.