Shot placement: critical
No matter which one you use. Saying that, I won't ever go back to mechanicals. I am not proud of the shot, but I have made quartering to me shots thru the shoulder with fixed heads, thunderhead, and deer did drop within 40 yards. I know I couldn't have acheived that same performance with a spitfire or rage. Sure, I shouldn't have taken the shot and it could have ended with me whining I lost a deer. But crap happens.
Get your bow shooting fixed well, and you won't be sorry. Lots of good heads out there, from grizztricks, to muzzy phantoms. Tough heads too at that.