Screen: Resistive. I don't care much about multitouch; I've used my Nintendo DS heavily since 2005 using stylus. Resolution definitely matters for me, more so than physical size.

OS : I enjoy using Maemo, I think having a "portable computer" is really handy. Of course, that is from the viewpoint of a power user/hobbyist programmer, and that probably influences my point of view a lot. Haven't tried/don't know a lot about other OSes (except playing around a bit with an iPhone, but not actually owning one).

Software Features/applications: Also using it as a phone is a handy "all-in-one" solution IMO.

Hardware features: Physical keyboard really helps a lot, I've figured, but I wrote decently fast with stylus on my DS.

That's mostly it for me. Should be noted that the only touch devices I've used (well, except for quickly testing something in a shop, or similar) is the N900 and the Nintendo DS. Also, I probably wouldn't be interested in a "tablet" as in the iPad kind of model, mostly since I don't find any need for it when I (more or less) have a computer in my pocket, with 800x480px resolution and decent hardware.