I have always used CMMG or Colt lower parts kits when assembling my AR lowers - because that's what was available. Is there a preference here amongst the more seasoned assemblers of AR lowers??

I usually use the BCM lpk's as they included the PNT trigger. I have also used the CMMG kit a few times and like those as well.

I have not used anything else as I have complete confidence in those kits and the CMMG is priced much higher than some of the "bargain" brands.

The last LPK that I got was a BCM and I'll just use those from now on.
The trigger is good and it came with the Mod3 grip which I like.

Another vote for the BCM kit for the already stated reasons.

I've had good luck with BCM, PSA, and Toms Tactical LPKs.

BCM and PSA are well known, but here's a link for Tom's Tactical: http://www.tomstactical.com/lower-parts-kits

I've used BCM and Stag over the years without issue

I don't use LPK's. I usually use Radian selectors, takedown pins (the captured detents are awesome), and mag release buttons, Geissele triggers, Norgon Ambi mag catches, and Colt bolt catches. For the rest of the parts (buffer detent and spring, mag spring, bolt catch plunger and spring) I buy them from the parts bin at a local shop. I find this minimizes the number of "extra parts" I have laying around.