If you absolutely must get a new MB or MBP, I think it boils down to what size you want. Either one can easily handle the tasks that you want it to do (including Sims and Age of Empires). The MB is considerably more portable, imho. But you sacrifice screen size and some graphics power.
The question is, do you value portability over graphics power? If so, get the MB. If you must have the bigger screen and better graphics, get the MBP (keeping in mind that the MB can handle the kinds of graphics needs you listed).
If you have a store nearby, I suggest you go and try them out, lift them up, see which one you feel most comfortable with. Fwiw, I did that yesterday, and came home with a new 2.4 MB. I was moving up from a 15" G4 Powerbook, and I really wanted something lighter and easier to haul around.