I researched this before I made my decision. For me it was about cost of ammo and being able to shoot inside during the winter or plink at metal on the pistol range.
Esentially I wanted two completely different functions from my .22 upper. I wanted something that could be used as a CQB rifle for shooting metal on the pistol range and something that could be used as a precision AR inside.
The kits: Well they all use the AR barrel so the twist rate is wrong. This makes it an unlikely candidate for precision shooting.
The complete uppers: There's only one available in Canada right now. At least that I know about. But they are pricey. Like the kits I've heard rumors of dependability issues. This seems to have been sorted out though and often the after market trigger groups were the cause.
The upper I went with was the Tactical solutions .22 Flat top varmint one. Free floated handguard, and a bullbarrel specifically for shooting .22 LR. The quality is good and this configuration easily allows me to put on my Eotech 553 or my Falcon menace 4.5-18x 56mm IR scope (with quick release rings). It should also be noted that the barrel is threaded at the end so you could add a compensator if you wanted to for speed/competition it may be a consideration although not really necessary in a 22.
I've only shot this rifle once and that was for plinking with the Eotech. So I don't know what it's accuracy potential is at this point. I'll have to order some of the 15 round mags in order to properly bench rest the rifle. The 27 round black dog mags are too long.
With an Eotech it's a lot of fun

. It's on my Stag lower right now. I have an Alberta Tactical one on order that will be dedicated for my .22 upper. Plus it gives me an excuse to keep the extra CTR stock I've been hording.