Aside from Sims 3, are you going to do anything else with it? Because the option between laptop and desktop really should be about portability. If you are not planning to be portable, then get a desktop b/c it is cheaper, typically more powerful and easier to customize and upgrade.
Sanity is overrated.
Nitromon is a type of Pokemon encountered in the Pokemon Nitrome Version series.
Desktops also tend to last years longer than laptops, overall they manage airflow and thus cooling better for those long gameplay sessions, and I for one would not enjoy simming on a small screen (although of course one can add an external monitor).
I agree that the only advantage a laptop ever adds is portability.