M&P 15-22. Love mine, or more correctly I did love it till my wife shot it. It's now "hers".
Seriously Bird, mine has been reliable as hell. Only hiccups it's had were ammo related and that's been maybe 3 rounds in 7-800. It's more accurate than me too. It's one rifle I have that I consider a keeper.
I put a cheap red dot on it so it's a lot of fun. Last time I had it out I put two rounds in a coyote exactly where I aimed from about 100' away and then 4 rounds inside the "Carrier" decal on an old window airconditioner from the same distance.
Sig 522. Several factory varaints out there. They eat all 22LR without any problems. Mags can be had for as low as $13 each. There have been reports of offset iron sights in the past but Sig will gladly fix it. Youtube any review and see what is reported. I run several Sig 556s so its a natural trainer for me as was its intent. It is heavy for a SA 22LR but this weight makes it handle like the big boys. Comes with a folding stock too. Current specs and pics are on Sigs site. Have fun
I will answer your question by saying my shooting buddies m&p15-22 is excellent and hella fun. Always accurate and always running like a top
That being said, I have a different option for you. I have a Chiappa .22lr upper that has been 100% reliable (excluding the time I had it mated to an NFA polymer lower, it didnt like that for some good reason, even with a mil spec trigger group installed. I chased this problem for some time including replacing the bolt to no avail. Finally did what I should have early on and tried it on a mil-spec lower and problem solved). The great benefit to my Chiappa upper is it mates to a STANDARD mil-spec real-deal AR15 lower receiver. Its not a ".22lr that looks like an AR", its the real deal baby. I have shot thousands of rounds through it, it has and continues to serve me well. I can reconfigure it and dress it up howsoever I see fit. I'd urge you to check out this option.
I would also suggest looking at taccom as they have some very interesting .22lr AR options.
Thirdly, CMMG used to (unsure if they still do) make some very dependable and respectable .22lr uppers
I have the S&W Ar15 also , LOVE it. I have the CCMG upper also lOVE it, I had a Sig 552 also , almost loved it, but it had a sloppy folding stock and I traded it . ALL 3 are great Fun Guns.
Vert true indeed but if you were going to get a stand alone .22 would the conversion upper and new lower been the first choice? Total price comparison? Benefit is if your big boy AR lower craps out you have a spare/parts. As long as the owner is happy life is good.