Personally I dont use MMS ... so no big deal there for me.

I have preordered the N900 and have an iphone 3G at the moment, my main reasons for choosing the N900 is because of its abilty to kinda multi task and open more than one program at a time, something the iphone is really no good at (yeah I know you can have a program open in the background, but not the same!)

I like many new buyers are keeping fingers crossed the N900 lives up to its expectations. Mind you I seriously doubt it will be an "iphone killer" (... is there an app for that?? ..lol..) The iphone has so many users and a graet little addition called itunes, with a never ending selections of apps/programs etc - something the Nokia lacks. I give Apple one thing, they have marketed the iphone perfectly - simple to use and all the toys you could ever want (and even more if you jailbreak it..) Basically it appeals to the masses, The N900 on the other hand I feel just wont have the same appeal.
Still like many I am looking forward to putting the N900 to the test and "hope" it lives up to all my expectations. In answer to your question, go for the Nokia..