I buy the KNS pack and then buy my springs from White Oak and use Sprinco for the safety spring.  I then buy my safety, trigger, mag release and bolt catch of choice.  KNS in my opinion makes the best feeling detents and their takedown/ pivot pins in conjunction with their detents are very smooth.  The KNS detent and Sprinco spring make for a positive feel with most safeties (FCD may be using this combo with their safety).

I have tried many different brands of LPK’s in the past and the above combo is what I prefer.

I use Damage Industries lower parts kits.  I have spare parts, and pick up the parts I need from a gun shop that stocks their parts (he gets them from DI's warehouse, which is a block or two away..)

I've used CMMG parts kits in the past, but never ran into a plastic mag release

I've also used PSA's kits several years back.

M&A parts was another go to years ago.  Prices were on par with most places at the time, and they shipped quick.  Sometimes I would order and have it sent the base "you get it when it gets there" rate, and received it the next day.

The best parts kit? One you put together yourself. You already decided you want one without a trigger or grip. Truth is, there are only a few more parts left. Pick what meets your quality and budget needs and go in that direction.