Someone not long ago asked about semi-auto 556 platforms and I came up with a list for them:
https://www.thehighroad.org/index.php?threads/semi-auto-5-56-rifles.
Beretta ARX 100
FN Scar 16
CZ 805 Bren
FN 2000
Keltec RDB
HK MR556A1
Steyr AUG
MSAR STG-556
Norinco 97NSR
Century Arms Golani Sporter Rifle in 556
VZ58
Saiga 556
ARES SCR
Bushmaster ACR (designed by MagPul as the ‘Masada’)
I feel if one is going to have one 556 rifle, make it an AR15, hands down. The design was ingenious, the linear recoil is unparalleled for control, easy to manipulate, good ergos that can be tailored to an individual at relatively low cost, parts are plentiful and cheap, and one can change calibers in 10 seconds with another upper. The design has been battle tested for 50+ years all over the world, by different countries, and has been updated and improved along the way.
There is no rival to it on the market currently.
Of course you'll be another lego user in a world of lego users, but there is a reason for that, in which all the haters of the AR don't want to talk about. Wild success and popularity isn't born out of failed and/or bad designs,
but bad implementation can plague a good design (yes the Stoner system had it's early hiccups; which were significant has been said to have lead to soldiers deaths, not disputing that) but in an organic environment such as a theater of war its obvious design changes have to occur with experiences. I understand the mistrust of the Stoner design by someone who fought in Vietnam as they saw it's origins which were troubled, but I attribute that to the military R&D not doing their due diligence before fielding a new weapons platform. One has to think that there has been 50 years of improvement on this design that we are afforded in today's AR15. Success of a product at the level the AR15 is enjoying is because it flat out works, and works well.
I also posted in another thread how there are different categories of AR15's available to the commercial market.
One category is budget, which with the advent of CNC, economies of scale and wide spread acceptance of AR's in the commercial world, the budget category of AR's is more than suitable for the vast majority of civilians. They are best served by buying a good value AR from a reputable company, and spending the saved money on ammo, red dot and training. With this one can put rounds through the AR, find any assembly weaknesses, upgrade the parts and end up with a very reliable carbine that has been put through tests all while training with it.
Another category is one that places reliability above all else, these rifles don't necessarily shoot the tightest groups but come with finishes and materials that have great longevity and reliability.
Then you have the purpose driven rifles that are built from the ground up to serve a purpose: lightweight, extreme accuracy, heavy courses of fire, long range, CQB, takedown features to aid in storage of firearm in small spaces, suppressed use, restricted states, etc.
Like I said before, it is my belief currently there is no rival on the market today for semi auto 556, anyone who says otherwise more than likely has a personal bias against the platform. There are far too many pros to the AR platform that cannot be overlooked.