Wow. I guess I shouldn't be surprised that this thread quickly scurried off in multiple vaguely-related directions! "I'm interested in a small caliber LONG gun, mostly for critter control" went to shotguns, 9mm handguns and armed robberies!
The advice given about .223 vs 5.56 vs .22 LR is correct. If you go for one of the .223/5.56, look for one that has the "Wylde" chamber dimensions (like Rugers). They will safely and effectively chamber BOTH, but do include just slightly longer "leade" before the bullet engages the rifling. This will adversely affect the accuracy a NEGLIGIBLE amount (unless you are professional benchrest shooter). The advice given about a decent-quality .22LR semi-auto rifle like the Ruger 10/22 is spot on. Very hard to go wrong with one.
But I, like you, looked for something with just a bit more capability than .22LR, when I go to grab ONE gun, either for hiking and plinking, or varmint control, or zombie apocalypse. I found from experience that racoon are tougher to kill with a .22LR than it would seem. Especially at night, in poor light, when they are moving around. I thought that a .17HMR was the answer, and actually bought one, but then returned/exchanged it for a Ruger Ranch Rifle (stainless) in .223/5.56. More than 10 years later, I still believe it was a good decision. I did have the trigger smoothed up, which makes it a wonderful gun to shoot. I added a terrific Weaver 1-3x20 scope (1x is AWESOME for most game shots - you can keep both eyes open with the SAME magnification for unlimited field-of-view). There are many that will say the Ruger minis are not accurate. Garbage. Not as accurate as a bolt bench rifle? Of course not.
For the same cartridge, ARs are fine, but I really like having a rifle that looks "regular" instead of "evil black". Plentiful, cheap ammo. 30 rd magazines readily available if desired. Winchester 64 gr PowerPoints make a respectable deer cartridge (IMHO). They look even better after a year or two of rattling around in the back of the farm truck to gain a little "patina".