Like Ken, it depended on when (and so what I had at the time to choose from), where based on habitat and the most common shots, and whim. So what was a "favorite" sometimes was not others. Only have 3 rimfire handguns left to choose from now... the HD Military would be first choice, then the OM Super Bearcat and last the OM Single Six 22MAG. Have used a lot of other rimfire handguns for squirrels, but can't say any of them were favorites.
Don't have pictures of all of these, so found some PD on-line of some of the rimfire handguns I have used for squirrels.
High Standard HD Military 6 7/8" 22LR from the mid 50's when I got it from my grandfather. Still almost as good as new.
Colt New Frontier Buntline 7 1/2" 22LR/22MAG I bought new that was my go to from the early 70's to early 90's, but I seldom used the 22MAG cylinder. Had custom stag, ebony and rosewood grips and a custom rig made for it.
Bullberry Contender 22LR Match w/Leupold 4X scope from the 90's that Fred built to my specs.
Bullberry Contender 17HM2 w/Burris 7X Target Scope from mid 00's.
AMT Lightning 12 1/2" 22LR in the mid 80's. Was a lot of fun but a PITA to carry.
Colt Ace Service Model Post War Issue 22LR in the 80's and 90's. I really loved this gun and was surprized how accurate it was. Sold it to a gent in Moscow (yep, the red one).
Astra Cub 22 Short in the 60's when it was all I had with me at that time while in the Navy. It had custom ivory grips on it when I bought it from my auto mechanic for $25. Did OK on squirrels if I could stalk close enough, but was better on the cottontails always in my yard (and the neighbors paid it no mind).
L.