I plan on buying a Gas Piston Upper in 5.56 in a few days.  I have the option to get a 10.5" or a 14.5" with a pinned flash hider to make it 16".  I already planned to build an AR Pistol while I send SBR paperwork out.  I have a 10.5" complete GI upper that I was going to use, but now I am thinking of selling that upper and doing my SBR as the Piston upper.  My question is what would you all do?  I really only planned to do one 10.5", so should that be GI or Piston?  Is there a benefit to having a 10.5" Piston Rifle over the pinned 14.5" or vise versa?  Thanks.

I'm a DI guy, but if I did a piston, it would be very short. The longer the gun gets the less benefit you get (even theoretically) for having a piston.

Topic Moved

This.

When you start going shorter than 14.5" and/or running suppressed the benefits/reliability of a piston system starts to shine. That being said there are a ton of guys out there that have had no problems with their 10.5" DI. My 11.5" DI has been flawless. YMMV.

I appreciate the 2 responses and hope for more. I currently have a GI Daniel Defense 16" rifle. I planned to have a 10.5" SBR once I send paperwork out and in the meantime I will run it as a pistol. I also planned to have another 16" or maybe 18". I wanted to have a gas piston as one of these options. It sounds like my SBR should be the GP by what you guys say. Thanks

If you already have a good upper you should just use that.

A 10.5 gas piston SBR depending on the piston maker will have a little less flash/muzzle blast than a shorty DI gun due to the way the gas vents. So a piston shorty can be a little softer shooting than a DI counter part.  
A 14.5 pinned gun you can take to any state without the SBR hassle and still is a 14.5 barrel that looks cool but little more practical than a 10.5.
Two pinned 14.5 one 10.5:

I have a  Adams 14.5 with a pinned Spikes Dynacomp...3-1  gun runs flawless an no SBR paperwork..

I have an Adams Arms 10" piston upper on a pistol....no tax stamp either.

The 14.5" pinned looks nice and so does the 10" pistol. I am waiting for the shop to get their 14s back in stock from getting pinned. Then I will compare the two and decide..I guess. I should just get both, but don't have that much now.