Have both, use both extensively.
If I am sitting on the couch watching tv, I prefer the MPA simply because it is easier to navigate.
However, to read books, newspapers, magazines, etc - iPad2 all the way.
For business use, I dont think you will find many people that use an iPad solely.
I personally have a Keyboard Padfolio I purchased at Brookstone for my iPad. I get out of my car and in my hand have an unbelievable tool that contains the internet, email, address book, iTunes, multiple apps, calendar, note taking capabilities, etc etc. Mobile nonetheless.
Comes down to content viewer vs content creator.