Hello!
I am trying to select a piston upper to fit my S&W M&P lower. All things AR-related are cheaper than dirt now days, so I may be able to pick one up cheap? I prefer factory built onece over the conversion kits. I am trying to stay under $1000
There are some listed on gunbroker under 1K. I Searched on AR-15 piston upper and sorted by price and looked at the cheapest five... Well four of them are Adams and one is POF.  The POF has a huge quad rail system and adjustable gas block, which I like. Is Adams a better brand? I googled POF, it stands for Patriot Ordnance Factory, never heard. Any recommendations?

Go with adams kit. There blem uppers or complete uppers for sale or on sale right now.

Like I said, I did not want to buy a kit. I am more interested in a complete upper that I don't have to fiddle with that already has the rail system installed. And I will be selling my M&P upper anyways, so I need a complete upper. POF uppers are like 1800 bucks new, but this guy listed for $760 on GB. My point is I want high end stuff (LWCR-like) for the price of el-cheeppo Adams... Reading about POFs i see that their Bolt Carrier has one piece goose instead of screwed on like regular AR has. Here is the GB listing
http://www.gunbroker.com/Auction/ViewItem.aspx?Item=431829212

Here are 2 complete Adams Arms Uppers that may float your boat:

http://www.adamsarms.net/16-carbine-tactical-elite-upper

http://www.adamsarms.net/16-carbine-tactical-evo-upper

Unlike that POF you linked on gunbroker, they'll be new and unsullied. Also that POF looks like a an old model, but I'm not sure.
Also the melonite treated barrels Adams Arms uses are, arguably, as good or better than chrome-lined barrels.

If you don't mind spending 300 over your 1000 limit, you can get a PWS upper. Here is an example on gunbroker

LOL, rather than "as good or better" I'd say "better or maybe much better".  QPQ has a higher rockwell hardness, lower coefficient of friction, and greater corrosion resistance all of which lead to longer life and less wear.  But that's just the physics behind it.  I can't speak to the emotional bonds people have with finishes.  

I won't say "You HAVE to get X brand."  That's up to you in the end.  But you won't go wrong with Adams Arms.  It's not a third rate or something.  IF you choose any other brand, you probably won't go wrong either assuming it's not a back alley knock off brand like LVVRC (ps that's 2 V's not a W) or Ardams Arms or Parrotriot Ordinarce...   You know some knock off trying to look like a name brand.

<nodding like I know to agree, because I do>  

The nitrocarborizing is superior to chrome lining in every way.  It's not a lining it's a treatment of the actual metal so it can't flake or come off in any way.  Everything said is spot on.  The only down side, if there is a down side, is of you want the look of stainless you'll have to have it ceracoated after the fact as all QPQed (Quench Polish Quench, btw) steels, be it CM, CMV, or stainless, all come out a shade of black, typically in the graphite range.  That makes sense if you understand the process as carbon and nitrogen molecules are trapped in the metal matrix when the metal is expanded through heating.  This functionally makes any carbon steel a stainless product without the Ni or Cr additions typical of stainless, but the process works just fine on stainless as well.

I guess if I had to mention an issue with QPQ it'd be more of the preparation process involved.  A lot of these barrels are button rifled (Adams Arms).  And that leaves minute burrs in the ridges.  If the barrel isn't lapped and polished correctly, once the QPQ is done those burrs are set forever.  Or at least as long as you'll be alive to notice.  So that polish stage is crucial to be sure the burrs are cleaned out correctly.  Less of an issue with a hammer forged barrel that is QPQ'd.  I'm not a hard core tacticalisious operatorizor, so you can take my comments for what they cost you.  I'm just a low speed high drag non-operator with a physics degree.  My personal perfect barrel would be a cold hammer forged QPQ'd barrel if you're looking for longevity and durability.

PS to the OP, check here:

http://lanbosarmory.com/index.php?main_page=index&cPath=12_23

Don't be fooled by the price listed.  Add stuff to the cart and you'll see a big price drop.  You might find something you like, cheap.

nothing wrong with any of the majors listed here, nor their coatings or surface treatments. it's really a question of dollars and features, unless you're looking for something specific...  I have Adams Arms, LMT, Colt, and Rock River Arms AR's and all are fine weapons of good quality.

I'd go with a PWS.  You mentioned that you have a S&W lower.  Does S&W offer their piston upper as a stand alone sale?  If they do, I would think that it would be a perfect fit.  AA makes the piston that S&W uses.  Whatever you do, avoid POF like the plague.  Not only is the customer service horrible, but the rail really does sit pretty high.  There are much better options out there and probably much cheaper as well.