iPad, Surface, Nexus, they're all good platforms that pretty much work the same. The real key is reliablity. In the three years using my company issued iPad 1, it's only crashed to the home screen a handful of times and never in a critical phase of flight. It's rumored we'll be getting the iPad 5s when they're released and I am excited for that. I just bought a Nexus 7 to do my non-work related reading, playing, surfing because my company iPad 1 is getting wonky when I try to do too many things (the apps have outgrown the hardware). In the cockpit I run just GoodReader for manuals, Jepp FlightDeck, and LogTenPro.
My concern with Delta and the Surface Pro is upgrade cycles. We're just a 1400 pilot group and we're already a year behind where we should be in the upgrade cycle. Will the Surface be able to maintain usability toward the end of it's life cycle as the bean counters decide when to allow deployment of updated devices?