Re: Daniel defense M4 or LWRC M6A1?
Are you asking about they're quality differences or about DI vs Piston.
I went with a LWRC a while back, I've since sold it and now have a DD v5. They're both good quality, so I doubt you'll be dissapointed with either. Piston, was always nice to clean even when shot suppressed. Honestly, most ppl would never know the difference. For the money, the DD's are hard to beat.
If you're stuck on a piston, the LMT MRP is pretty slick with the barrel swap ability.