I can't make any comments about the Mossberg. I've never even seen one. I do have experience with the Colts and Smiths. I really don't think that either is appreciably more accurate than the other. I'd suggest that you just list the pros and cons of each and get the one that has the most pros for you.
I got the Smith. My reasons for doing so were that the Smith's magazines are readily available and not expensive. The Smith is made mostly of polymer similar to that of the Glock. It's tough stuff. Although the Colt is made of metal, it isn't any sort of aluminum or any thing like that. From what my research told me, it's made of some sort of pot metal and I felt that the Smith would be more durable in terms of being able to survive drops and knocks. From what I've seen, pot metal is pretty brittle.
A major thing for me was that the Smith also accepts standard AR15 trigger groups. I'm running a Geissele SSA in mine. Totally not necessary, but it does make the shooting experience more enjoyable.
I know that many say that the Smith feels like a toy and prefer the heft of the Colt, but the reason that I got mine was because I wanted to use it for more than just range duty and because it looks cool. The Smith is so light that you'll almost forget that it's slung across your back until you need it.
As for the alleged functional problems posted as they relate to both the Colts and the Smiths, I believe that both have had their problems, although I believe that the Smith has a bit of a better track record.
I've had mine for a while now. I got mine out of the first shipment that my LGS got of these when they were released, so mine doesn't have the threaded barrel. It is a bit picky about ammo, but found that it runs flawlessly on Winchester Expert bulk and any other premium ammo, like Mini Mags.
After everything was said and done, however, if I had it to do again, I'd probably put the money into a CZ or Savage bolt gun, if I was just committed to spending that much money. These days, when I need a handy .22 to take into the woods with me, I usually just grab my Henry lever gun. It's small, compact and no mags to worry about.
The .22 ARs are built to mimic a real AR. What this means to me is that it is bulkier than it needs to be and uncomfortable to carry around, weight notwithstanding.
Still, if you're just dead set on getting an AR in .22, I'd go with the Smith for the above reasons.
Good luck and have fun.