I'm looking for a .22LR plinker... looking for feedback on the Colt (Walther) or the S&W... which one?

S&W, the colt is a cheap pos that colt had no part in the manufacturing of (that I'm aware of). Never the less, it's a pos.

THIS. If you research this you will find that the COLT M4 is a Walther Product imported by Umarex and Colt indeed had nothing to do with it. It has been plagued with cycling issues and has proven highly problematic and unreliable. As a side note, the COLT M4 has a plastic adapter that slides over the thin inner barrel. The 15-22 by way of contrast will eat anything and everything and asks for more and has a solid steel barrel.  I have one and absolutely love that rifle!

I had the longer barrel m16 version, and while you couldn't interchange parts with your other ar's I felt mine shot well for keeping iron sights on it. I only had cycling issues when I first got the gun and then I adjusted the recoil spring to allow it to return to battery with more force, and then the issues went away. It was accurate enough, though I never shot for groups with it, but it would hit clays at 50 yards with no issues. My biggest gripe was the trigger wasn't great by any means but it was easy enough to shoot with. I would try to find someone that will let you shoot both, and let you decide that way. I liked the fact that it was still aluminum receivers on the colt and didn't feel cheap.

I don't have any experience with the Colt so I cannot comment.

I did shoot a friend's M&P with no malfunctions.  I liked the gun, felt great, and shot well.  Lots of fun.

I like DPMS and purchased their .22 upper and prefer it far more than the M&P.  It was cheaper in cost than the M&Ps I found, but you obviously need a lower.  I have about 600 rounds through my DPMS upper, using Black Dog mags and I have had no issues.  I have used iron sights and a scope with good accuracy.  I've used Remington Yellow Jackets, CCI lead round nose, CCI hollow points, Federal Lighting, and Federal bulk pack.

When I first got the upper I had a handful of Remington Thunderbolts and Winchester Wildcats (maybe some other stuff that I couldn't identify) that didn't do well.  I don't know if it the upper needed a break in or had a problem with the ammo, but after those rounds were gone (probably about 30-40 rounds) I've never had another issue.  Black Dog mags run about $13 - $18 depending on where you buy them.

Never shot the Colt. Looks nice, but have heard all the discontent as well.
M&P. Can't imagine there be a more reliable fun rifle. Shot thousands of rounds through it. We shoot eggs and shotgun casings at 60 yards all day long with MBUS sights. Only FTF problems are from shit rounds with high failure rate like Thunderbolts.
Want to buy another to customize, but other things keep preventing me.

I own a "Colt" M4 .22 carbine and have not had any trouble with it what-so-ever. I shoot it with CCI sub-sonic and Standard vel. with a can. It has ran 100% and is very accurate. IMHO it's much more substantial than the toy feeling S&W.

Hell mine was even Bubbaed when I got it. Some tool cut the front sight tower down to put a big honking scope on it. I replaced it wit a AR gas block/sight. The hand guards were replaced with a old alum. CAA set.

Get the S&W. I have about 4000 rounds through my 15-22, not a single failure except one jam but that was my fault for not loading the first mag right the first time I took it to the range. The gun has been flawless, and i only clean it every 1000 rounds. Eats anything I feed it, and I don't know about tack driver, but I shoot my 15-22 accurately and consistently with a vortex strikefire out to 300 yards, clay pigeons, soda cans, etc. IMO it is an exceptional gun and value for the money.

I have the Sig 522 combo kit and love it.  I just ordered the $200 American Tactical AR15 upper from CDNN.  That's about as cheap as I've seen a full conversion setup.  Hope it's as advertised.

The 416 is made bu umarex too. It is blessed as being reliable and accurate.

However the M&P crowd bashes it becasue it doesnt have a working bolt release. I'd rather have a milled aluminum receiver than a working BHO release on a 22 plinker.

I've heard about the issues with the colt, but I've not seen them first hand. Frankly if I wanted an AR style 22, Id get the 416 or the M&P.

I bought my Umarex / walther / HK 416 for 299.  Having handled both, I'll take the 416 for a dedicated 22.  - Also the mags are cheap. $20 each.

I have an M4 Ops, and its worked fine for me.  Never had any functioning problems.  I have never tested it for accuracy, just a plinker but it seems OK.

Get the 15-22.  It's excellent right out of the box, and if you feel like customizing, there's a pretty good aftermarket...  Since it's still in my buffer:

15-22 mock dissipators I made:

Dang, they are sweet.
Do you have a build thread somewhere?
Love the forearms.

I have the Colt M4 version. I bought it used. Its accurate and runs great. No FTFs or hiccups whatsoever.

the only negative about the 15-22 is the feel- its mostly plastic and as a result, its very light/ toy like, just like someone above said. Holding it in my hands for the first time was a huge turn off for me. other than that, the 15-22 has a lot of good things going for it. If budget isnt a concern, assemble your own.

Dealer friend sold 4 of the Umarex Colt 22s.
All but one came back. Mine runs great, but apparently it was the only one.
YMMV