No matter what gear I'm looking for, I always consider the options carefully and make my decision based on a few key criteria;
1. Can this "object" perform more than one function
2. Is this as compact as I can get it?
3. Is it suitable to the environment?
4. Is it robust enough
5. What does it cost?
Foremost in my mind is versatility. When I'm working I can carry a few bits and pieces with me, but I'm past the age and inclination to be a pack-mule. I like to carry small things that can do multiple actions. So when it comes to knives, I prefer utility and extra functions over a nice blade. Sure the blade is important, but I'd rather have a folder that slips onto my pocket and has a window-breaker on the end over a pretty blade that needs a holster on a belt.
If I can add a screwdriver head on the body of it somewhere- that's a plus. So for me it's always going to be a folding knife with a little ingenious design into the handle and how its made. Then it's onto the locking mechanism and coating of the blade. I work in the rain quite a bit, so I don't want something that will rust or has a cheapo opening mechanism that will gum up quickly in bad weather (or sandy pockets.)
A grip that has grooves for my fingers to help acquire a nice firm grip is never a bad thing and of course if it's got a stippled grip for added durability in lousy weather then that's even better - top marks right there.
I'm not a brand slave by any means but I've had great joy out of Spyderco blades for years now. Obviously Kershaw if you have the extra cash is a great buy and there are plenty of nice folders available for a few hundred Rands. Take your time and weigh the blade in your hand, see if it fits well. Decide if you'll carry it left or right side and make sure the clip is adjustable while you're at it.
Check the edge on the blade to make sure you can sharpen it up now and then. Cheap chinese blades have 1mm edges that aren't able to be sharpened and are considered throw away blades after a few months use.
If you're a multitool person - that's fine by me, just make sure that the blade is easy to get out single handed - You never know what the other hand could be busy with at the time.