In my opinion, iCloud makes owning an iPad and iPhone together a stronger combination than mixing up OSes and hardware. You literally just log in to your iCloud account once on all your devices and everything stays in sync seamlessly.
iCloud for document sharing isn't the only service integration that's helpful, either. I'm in the medical setting, and many members of my team use iPhones (texts go through iMessage). I'll be working on my iPad Mini and can see and respond to the text messages straight from there, without having to take out my phone. It's incredibly convenient. Unfortunately there are enough Android users that I still have to resort to the phone for standard text messaging at least a few times throughout the day
For
Joe1, though, the issue is slightly complicated by the fact that we don't yet have an iOS version of Microsoft Office (although according to the rumors, it's coming). Sure, we have Keynote, Numbers, and Pages, but those can introduce some formatting issues when viewing and editing Microsoft Office documents. Heck, there are even minor issues when going between the iOS and OS X versions of those programs. If his work wouldn't be affected by that then it's a viable option, as it sounds like everything else he needs would be covered.
People here are going to hate on the Surface (no big surprises), but I honestly think it's a pretty nice device. If I weren't so firmly entrenched in the Apple ecosystem I'd be all over it. It's up to personal usage, then: would
Joe1 (or anyone making a similar decision) benefit from the tighter integration between devices? If not, the Surface is technically a more capable device than the iPad, and going from a Surface to an iPad might be a downgrade.