Thanks for bumping this Ohio Archer. I had missed it somehow.
mattruthluke, my answers are going to be somewhat generic because I don't own a mossberg 22. For the big reason that although they may be smiliar in appearance to an AR15, they are far from being an AR15 in 22LR.
If that is what you're looking for, you can either get something like the ATI 22LR, or S&W makes a dedicated 22LR, as well does several other companies.
OR
You can buy a .223 AR15 and 22LR conversion kit that simply replaces the 223 bolt and magazine, which is the option I chose because that was all that was available years ago in 22LR when I bought it. But in the long run, that option still gives me the most options.
OR
You could get a Ruger 10/22 and put an archangel style stock over the ruger, which is essentially the same thing as what mossberg is doing with their AR15'ish line of guns.
As for which 22 ammo is the cleanest, I'm not really sure. They're all kinda dirty in my opinion.