Accuracy and reliability should really be discussed separately.
A complete .22 AR, or an upper, or a conversion is not going to have a match or Bentz chamber so they will not be as accurate as say a Kidd or Fedderson. Then you have ammo...the match ammo is optimized for the match chambers so you don't get the same benefits in an AR.
As for reliability, go get your map!
The S&W AR-15/22 has been proven to be very reliable. The Mossbergs I know of have not bobbled much, but they are newer and I have not seen as many of them. The uppers, the Nordic is far and away the best of the bunch, but they have trouble keeping up with demand. The TacSol and CMMG complete uppers would be 2nd and 3rd and worthy of consideration...but I'll just stop at only listing three.
I have never owned a "stock" 10/22. All of mine are ground up builds and all are extremely reliable. My Marlin 7000 and Volquartsen auto rifles are the best in the accuracy department with match ammo. The Tacsol barrel on the custom 10/22s is a tad behind, but still more accurate than the AR15-22 variants.
For my purpose of rimfire matches used to hone speed rifle skills for 3Gun, the Nordic upper is also the best bet because I have it on my backup lower with the same stock, grip, controls and trigger as my match rifle.
Just DON'T get a bolt conversion. The accuracy and reliability are not there in general and they become a frustration.
There are no downsides, just differences that may make one better or worse for you.