While my knives are used primarily for utility (and I'd imagine most people would say the same), I select them based on their suitability for defense.
Here are my requirements for any knife that I buy:
For folders: (for the record, I'm currently carrying "waved" Gen-3 Spyderco Enduras)
-Good Locking mechanism: I prefer either a frame-lock or a spine-lock. A liner-lock, for me, is a deal-breaker (too many bad experiences, just don't trust them).
-Overall shape/design: The shape of both the blade the handle have to be conducive the "grips" that I use (primarily "Pikal," but I also like the Saber grip). This usually means a fairly "neutral" handle--without a lot of finger-grooves and stuff--and a blade shape that puts the point at or below the centerline (i.e. spear-point, wharncliff, drop-point).
-Opening Mechanism: I've become a convert to "waved" folders so any folder I buy as a "primary" has to be waved, or "waveable" (tip-up carry with a hole. i.e. many of the Spydercos,the Benchmade Griptillian, etc.)
For Fixed Blades: (once again, for the record, I carry a double-edged CRKT Companion and a small reverse edge knife similar to the ShivWorks Clinch-Pick). My "backpack" and/or camp knife is a K-bar
-Once again, blade and handle shape
-Good sheath (an easy fix if it doesn't come with one you like)
-Uh yeah...the other stuff like locking mechanism and opening mechanism don't apply...I love fixed blades
I don't really pay much attention to the type of steel used. Most knives from quality manufacturers are going to be just fine. That said, I really like the VG-10 that Spyderco is using now. It takes a wicked edge and seems to hold up well to extended periods of use.
As far as serrations go...it depends. For a utility knife that's going to be put to heavy use (lots of rope cutting, etc.), they're great. Otherwise, I'd just as soon stick with a plain edge.