I'm shooting the new Montec G-5's. Fixed blades. These things seem nearly indestructable. They are a 1-piece stainless molded head, with blades that have very thick bases and taper towards the cutting edge. Pretty expensive head, but since they are re-sharpenable, I could see a person shooting 20+ deer with one head. I've got 4 this year on my current one.
Before these, I shot Wasps Hammer SST's and was very happy with them. Fixed blade all the way. I've heard too many horror stories about mechanicals to even consider using them.