Zombie; you must seriously have the worst luck in all the world. My M&P15, as well as 2 others I turned friends onto, are perfect right out of the box. Including the triggers. Without having scaled it, but comparing it to many of my other rifles; some of which I have scaled and done trigger work on; I'd say that my M&P15 out of the box right now, is shooting with probably a 6lb trigger pull. Give or take. Very little if any play. Crisp. I love it. I wouldn't even consider having the trigger worked on.
The M&P15 is probably the best when it comes to ammo. There isn't 1 brand of ammo; brass or steel case; that this rifle won't shoot accurately and reliably. It's perfect.
The majority of posts, reviews, comments, etc... that I read "Prior to purchasing" this rifle, seems to share my conclusions. That's one of the reasons I waited for a good sale, and I bought this rifle. I didn't just walk into a shop with money burning in my pocket. I researched various AR's for about 6 months. I wouldn't spend the normal $950 on this AR, but I knew that if I could find one at the right price, that it would definitely be the gun I wanted. I found it on sale about 60 miles away. I noticed it on a road trip coming back from Denver Airport picking up my wife. When I saw that I could save $300 on it; after doing all the research; I definitely was buying it.
I've had it about 4 1/2 months now, and have close to 2000 rounds through it. 90% steel case mix of wolf, MFS, Bear, Barnaul, Tula, and Herters. The other 10% is PMC Bronze, Hornady TAP, and mil-surplus 5.56. The rifle will shoot anything you feed it. The only modifications I've done to it was to add a set of iron sights to it, (Yankee), Added a 2x red-dot, (A1optics), and also a ST-T2 buffer. Other than that, it's stock. I haven't had to mess with triggers, BCG, or anything. I average around 5000 rounds a year through most of my non-hunting rifles. That may not seem like much, but with about 5-6 rifles, that's about 30,000 rounds. I'm sorry you had a bad experience with your M&P15, but you're definitely one of the exceptions.