More than anything else, this would be the killer for me. It's one of my biggest beefs with the iPad, is that you have to jump through all kinds of hoops to attach external storage.
Screw that. I like being able to pop out an SD (or microSD) and either take stuff off, put stuff on, or swap it out for another one.
Then the iPhone is definitely not for you either. But so far in my experience with my Android, I still haven't had the need to pull out my SD card.