Between the different types of "piston" driven AR uppers - these are the two that I have heard of the most other than the civillian-untouchable HK-416.

I would like to get readers perspective on which one is "better" and why?  I know the difference in cost is going to be about $150 give or take.  But I really want to know if anyone out there has tested/compared these uppers? (or their assembled rifle counterparts).  I'm a technical geek when it comes to this stuff, so the more stuff you guys pour on, please give me the complete low down on each.  I mean if you want to get as technical as to which has the better "head spacing" - LET FLY!  Much appreciate!!!

Well, as far as the piston system goes, POF and Troy are one and the same.

Do they use the same internals?