I'm a qualified AR 22 Junkie and I have three dedicated 22 uppers and a couple of conversion kits. This is a great time to be buying a 22 AR upper as there are a lot of products on the market. CMMG is probably the front runner right now and offer several options including bolt hold open magazines and different barrel lengths. The CMMG uses an Atchisson/Ciener pattern bolt as does Model 1 sales and Spikes who just recently re-entered the market. Tactical Solutions has two or three uppers but are more expensive than CMMG. Armalite supposedly is offering a copy of the CMMG with their name and DPMS just entered a new designed bolt for their dedicated 22 AR's and is very similar to the Nordic designed bolt for their uppers. Not so well known are 22 uppers offered by Joe Bob's out fitters manufactured by Kies and Center fire systems is offering a barrel bolt combo. Chiappa probably has the cheapest upper of the lot and uses a polymer upper and some short cuts in production to make their upper cheaper. Hess has a 22 upper listed from time to time on gunbroker and uses different names shipped out of Minnesota. Of all these the only two I wouldn't buy would be the Chiappa and Hess/Vulcan/Blackthorne/Velocity.
As far as best I'd lean towards CMMG and Tactical Solutions.
As far as best I'd lean towards CMMG and Tactical Solutions.