You truly have to see each one in person to get a proper sense of one over another that could meet your needs/wants. The operating systems differences alone might be a deal breaker for some. For the record, none of the phones you've listed are *great* at multi-tasking, in the sense that it really does a good job of replacing a PC/netbook/laptop.

What I suggest is you get your hands on at least two of them and report back with specific questions on their functionality.