Sorry for the diversion.
OK, my choice is based more on my hunting style than anything else. I would rather range & explore the woods while hunting. I'm not much for sitting & waiting for squirrels to show themselves so I can take careful aim.
So my choice is not a rifle at all, but a side by side shotgun. I wish it was a flinter, but it is a cap lock. I like it because it is an original dating to about 1870, and it gives me some sort of satisfaction that I'm keeping this old gun in use.
I hunt by walking the woods looking for squirrels ahead, and then stalk them. When they see me coming (and they always do) I charge ahead, and they usually run giving more of "bird like" shot rather than an aimed shot. The relatively short length (45" OAL) gives me greater mobility while I'm making that charge.
Back to Rifles: I have done the sit & wait method, and used my .45 flinter in those cases. I prefer long barrels. This one is 44 inches. It is my opinion that a long barrel does not necessarily give the gun greater accuracy, but the longer distance between the sights gives the shooter a slight advantage in aiming.
When taking an aimed head shot at a squirrel, I don't feel that the ball size matters at all. If you hit them in the head with anything moving that fast they are dead. And I don't eat the head. I will concede that if you miss to the body side, of course you will tear up less meat, and the smaller calibers make for much nicer pictures at the end of the day. Larger balls also give you an advantage if you try to "bark" a squirrel whose head is not visible. I could be described as more of a bull-in-a-china-shop as opposed to finesse person, and I would probably break ramrods for smaller calibers way too easily.
There is also the pair hunting style that is somewhere in between. Here a partner/dog/grand-kid chases the squirrel around the tree, while the shooter waits quietly for a shot. I have not tried this method personally, but I would imagine that shorter barrel lengths may help with maneuverability in this hunting style.
As for stocks, my preference is for full stocked rifles. I like tiger striped maple the best. The choice should be influenced by your persona, but a man of any means could have saved/traded-up for his dream rifle. Mario might disagree with that point.
If you buy/build whatever type of gun you want, it will subconsciously give you greater confidence which is in turn likely to lead to better results. So while it is wise to ask, you will only be getting opinions, and ultimately you will need make the choice that you feel is best for you.
Good luck, and be sure to let us see a picture of your first squirrel alongside your new gun.