Sounds like you're on a limited budget.
Let's assume that you'd have a blast playing games on either platform. So the fun factor is equal for the base hardware and they both have an equally fun library of games for you right now or in the near future.
By the time you've scraped together enough cash for a PS3 and one game, you could have a Wii and a half-dozen games. Basically I'm saying that if the conditions in the previous paragraph are true, the fun per dollar of the Wii platform would be better than for the PS3.
Now you have to factor in your personal preferences. If hi-res graphics make things more fun for you, you might be satisfied with having a PS3 with fewer games because they're shinier. If excellent motion controls make things more fun for you, the balance shifts more towards the Wii. The content of the games libraries might also influence your decision, if you simply must have MGS4 or if you hate Mario for some reason.
"The worst part about these reviews is they are [subjective]--and their scores often depend on how drunk you got the media at a Street Fighter event." — Mona Hamilton, Capcom Senior VP of Marketing
*Image indefinitely borrowed from BrainBoxLtd without his consent.
