I have used both, this year I'm back to fixed (muzzy mx-4). I just like the idea of less moving parts. I have used spitfires and tekans both with good results. Only problem I had was that the tekans would sometimes catch on my quiver and open when I was taking an arrow out. I have killed deer with, thunder heads, tekans, spitifres, muzzys, G-4's all with no problems. I just wanted to change this year so I'm trying the mx-4's. I think I prefer fixed though, just think they look cooler and that's what really matters right?