I've been to both, luckily. I will say the Cedar Point etches out Magic Mountain, Magic Mountain does have a few roller coasters that stand out like X2 and Viper (highest loop in the world I think). Deja Vu is pretty nifty too. But all of Cedar Point's roller coasters are great. I'm gonna have to put Millenium Force on top of Maverick though personally.
There are so many rides now that are better than Millenium Force. Check out Intimidator 305 at Carowinds. When it opened though, Millenium Force broke quite a few records and was undoubtedly the best coaster in the world but times have changed. The manufacturer who built Millenium Force, Intamin, has since then built smaller versions, in essence, of Millenium Force that are so much more forceful. (You can look up Piraten at Djurs Sommerland as an example.) But having said that it's still a great ride!
I personally feel Magic Mountain has a better collection of roller coasters (Riddler's Revenge, Tatsu, X2, Green Lantern, Superman Escape From Krypton, Revolution) but as an overall experience Cedar Point is so much better.
EDIT: Wow, we are getting off topic!