I'm with the group that says revolver if I had to depend upon a rimfire. They can be notoriously unreliable, and if I hit a bad primer, I'd rather just pull the trigger again than have to rack the slide while potentially under fire.
I have always been a big fan of both S&W and Taurus revolvers, and the new Ruger LCR is quite interesting. I'd probably go with the lighter aluminum/scandium options if I went S&W or Taurus (better for carry, and in .22lr or .22mag shouldn't be bad even for hand/wrist issues). While I do love S&W, I'd probably go with the Taurus at around $300 less or the Ruger at $200 less for the lightweight versions.
I'm not sure if I'd go .22mag or .22lr. The Ruger doesn't seem to be available in .22mag (per the website), and the .22mag versions of the S&W and Taurus revolvers have one fewer round. One more round, or a little more power per round is a tough call. I'd lean towards the Taurus because it has one more round than the equivalent Ruger and S&W (8 rounds v. 7 in .22mag, 9 rounds v. 8 in .22lr). Since neither is a particularly strong caliber, and expansion is likely a hit or miss proposition, I'd go for penetration v. expansion. I'd want LRN over HP, a heavier bullet, and a high velocity round. If I went .22lr, I'd probably get 40gr CCI Mini-Mag or Winchester Wildcat.