its a hard decision im at level 65 and i dont know if i should start all over again just for a new rank i have so many cool weapons i jjust dont know *cough* M2 Flamethrower
Well it depends dude. If you wanna unlock everything, just stay at 65. If not prestige.
Right now I'm level 15 2nd prestige. When I got to 65, I prestiged just to see how it would be like. I got to 65 again, and even though I had all the weapons and classes, the game got boring, so I prestiged again. I had completed most of the challenges, but after I prestiged, it didn't really bother me.
I suggest you stay at 65 for a while and when the game starts to get boring, prestige!