Opinion please. The new Stag15 3Gun Elite or the new Ruger AR 5.56MPR and why? Currently leaning towards Stag. Will have an optic. Mostly 100-300 yrds with occasional 500yrds. Steel plates and occasional hunting varmint eradication. Looking for longevity and reliability. Thanks!

I have no experience with the Ruger but had a Stag Arms left handed 3G rifle and it was 100% reliable.  The Geissele trigger is awesome, mine was VERY light.

You really need to compare the components of each rifle because they are different (i.e. Stag has a stainless fluted heavy profile barrel, Geissele trigger, etc).  And of course the price point is totally different too.

If price doesn't matter then it's just you choice of components in my opinion.  I've owned Stag Arms throughout the years and have never had any issues with their rifles.  I now own Black Rain Ordnance because they started producing left handed AR15s and I wanted mid length gas systems rather than carbine.  But I am considering another Stag Arms 18" AR15 (the new Texas version that is similar to the 3G but a different buttstock and trigger....I'm going to change the trigger to a Black Rain Ordnance drop in trigger like my other AR15s and also the buttstock so I have no reason to pay more for the regular 3G Elite model).

I have no experience with customer service (i.e. having to send the rifle in for warranty work) but the Stag is lifetime and transferable.  I don't know about Ruger although I've "heard" their customer service is fantastic.

I'm sure others with more experience with both rifles will chime in.