I've got a stripped lower & 2 stripped uppers on the way. Having a hard time deciding what to build. I was thinking something along the lines of an A4 style flat top 20" barrel w a quad rail or a updated 629 style commando w the 11.5" barrel w grenade ring & moderator. The typical do both is an option but the other upper might get saved for an SBR but im not sure yet. What does the hive think?

Good question, FF.  I recommend you build the lower as your one and only, configured to suit your ergonomically.  Then build one of the uppers in 5.56 with the 20" barrel you hanker for, and build the other upper in 6.8 SPC, a lightweight 16" carbine.  The 5.56 needs a longer barrel for optimum performance, while the 6.8 does just fine with a 16-incher.  

FWIW, that's the route I took.  My 5.56 build has a low cost 1in8, chrome lined barrel from Green Mountain and its an amazing tack driver.  The pic below is how the 5.56 ended up after much parts swapping. good luck - CW

Actually Ive had a 16" 6.8 for about 4 years already. This is actually going to be #4 that I currently have.  I've got the 6.8, 2 in 5.56: a 18" SPR, & a 14.5 w permanent flash suppressor.