I have
this mini folding bluetooth keyboard (you can find the same thing on ebay for cheaper). I like it because it's so slim and compact, I can stick it in my bag and forget about it. I usually use it with my Nexus 7, but all you really need to type is some sort of screen and a keyboard, so I don't see why I couldn't use my DNA instead.
I've tried a bunch of different productivity apps (Kingsoft Office, OfficeSuite Pro, QuickOffice Pro, Evernote, etc.) but my favorite is just Google Drive--it recognizes multi-stroke keyboard commands (e.g. CTRL + Z) which is invaluable. On a tablet, Kingsoft most closely resembles MS Word, and most formatting stuff is just a click or two away. The paid versions might have features that the free apps don't have, but I haven't stumbled on any that I needed. OfficeSuite Pro syncs better with cloud storage, but that's really the only thing I can think of.