OP I think you shouldn't have asked that question on this website seeing as most of them are PC fanatics and wont answer your question.

IMO i would go with PS3 i heard for X-Box 360 you have to pay

7.99 per month if you purchase it monthly (not suggested)
19.99 per 3 months (again not suggested)
49.99 for 12 months (suggested).

On the other hand for ps3, Online is completely free.

I suggest the ps3 hope this helped.