Pretty much any decently lightweight scope will do. Don't know how dark or overgrown your squirrel hunting places are but in general I'd recommend at least a 36-40mm objective just to help with the resolution, all else being equal.
Some fwiw info - any Leupold 3-9 scope with their standard duplex reticle will give you a precise 100 yard aiming point. At 9x that reticle covers 6 MOA point to point which means the tip of the bottom post is 3 MOA or 3" at 100 yards below the crosshair. A .22 high velocity bullet sighted in at 75 yards drops right about 3" at 100 yards.
Also, 3 MOA covers 1.5" at 50 yards which just about coincides with the mid range trajectory of that .22 bullet sighted on at 75, so you can get a good enough aiming point at 50 yards by holding just below the top post.
If you find a scope you like but it has a longer parallax setting than you want, you can change that. Never done it myself but offer this link as a public service, or menace as the case may be.
Changing Parallax On a Non AO Scope Yourself?...I was wondering what would be the rimfire scope of choice if you could only pick one scope for rimfire use. The use would include informal target shooting, Squirrel hunting, and just all around plinking.
Can't stick to just one scope but to sort of answer your specific question, I've gone with two scopes for general purpose shooting. A Leupold VX-II 3-9x40 centerfire scope with duplex reticle is on a CZ 457 American for the reason mentioned above.
My two "informal plinking to 200 yards" rifles both wear the Leupold VX Freedom 3-9x40 with their Rimfire MOA reticle. It has a 60 yard parallax setting and the reticle has 25 hash marks below the crosshair in 1 MOA increments, that's 25 MOA total holdover which is plenty enough out to 200 yards. The view is bit busy under the crosshair but within 75 yards you just use the crosshair anyway.
"Serious" rifles all have SWFA 10x40 scopes with mil quad reticles, but those are large and heavy and not something you really want to tote around a lot.
