S&W makes a fine AR-15. I've carried one for work for better than 8 years now (I've also carried a Colt in the past). My work S&W MP AR-15 probably has upwards of 10,000 rounds through it, and gets used as a utility weapon in the field. It runs just fine, and has never failed on me. I had to replace the safety detent about 1,000 rounds back (safety was sticking in the "FIRE" position), but it has been flawless otherwise. The Colt I previously carried was a fine gun, too.
Honestly, the AR-15 has really taken off in the last 20 years. I'll agree with others in saying that the Colt fan boys are demonstrating some serious brand loyalty, but it certainly doesn't meant that's because Colt makes the best AR-15. There are a lot of great AR-15 manufacturers out there these days, and Colt is neither the best or worst of the bunch. A LOT of companies make good AR-15 rifles these days, and it's hard to know what you really want until you get some time behind one.
If you can't get the opportunity to shoot a few AR-15's before you buy one, then at least try to think about what you might enjoy shooting the most. I have several AR-15's currently (and have had others in the past). Each gun serves its own role in my fleet. The shorter barreled guns (including an actual NFA short barreled rifle) are great for defensive use, and in situations where a short length matters. But, the gun I really enjoy shooting the most is a 20" barrel A2 style AR-15 that I bought back in the 1990's (when the government was still making us crown barrels and grind off bayonet lugs for "safety"). Anyway, that gun just has a perfect balance in my hands, and has been the most accurate of the AR-15's I own. It's an open sighted gun that I just enjoy taking to the range. But, it's not the ideal home defense gun when compared to other AR-15's I own (or have owned).