I was looking at a few different brands until I finally bought my S&W M&P15 Optics Ready a few weeks ago. This is my first AR. I've shot several other brands before. Have some family friends that own S&W's, my dad has a Rock River Arms, shot bushmasters, and was considering a DPMS.
I usually do a month of research before I buy. I browse several forums and read up personal and professional reviews. When it came time to buying one, it was mainly between the S&W that I just bought or the RRA. I wanted quality, value, reliability, and stay within $1,000 (I know, crazy thinking during the current state of the industry).
Anyway, a few weeks ago I started calling LGS's and started losing hope that I would find a Smith or RRA, let alone any AR-15. Last place I called put me on a waiting list and then called me a few hours later and told me they had the exact Smith I wanted brand new in the storage area. Went there the next morning and only got stung $950. Got the AR-15 I wanted and paid below my max; it was a perfect situation.
So I chose Smith & Wesson because of availability. But mostly because of my personal experience with the weapon, the thoughts from the people on this forum and the professional reviewers. Plus Smith's warranty is the icing on the cake.
Hope this helps. Nothing wrong with cross shopping and going on several sights that are biased to one brand. You are bound to find objective thoughts.