I've sorta been on the fence between the two and it really depends; Googles services aren't guaranteed to work 24/7, neither are Apples. With MM though you get something thats essentially designed to work between your Macs/iOS devices, as well as provide you with not only e-mail but other services as well. Having said that though you can get the same level of functionality by using dropbox, logmein, picasa, and googles sync all of which can be setup for free.
In terms of ease of use, if you already use a mac and have an iphone, I think MobileMe is the better option since it tends to integrate well with everything in the ecosystem without installing extras and is very easy to get going; it also tends to work correctly with the OS X base programs.
Keep in mind that once you sign up for a trial I dont believe your account is deleted of for some period of time (I could be wrong though)...I signed up for one a while back and then tried logging in to find it still working a year later asking me for payment. If you sign up now and it ends up becoming free you might be able to still access it if it does.
The one thing that I have noticed that is definitely messed up is the iDisk function in the finder; you can however get it working fine by using something like Transmit (which unfortunately requires you to spend more money though).
I guess it all comes down to if you want a nice integrated package, then use MM; if you don't mind using several different services and cost is an issue, then go with google/everything else. I think it really comes down to personal preference...