Well, here's what I've used in the past...
Shotguns: Mossberg Model 500 in 20 guage, SxS double barrel .410
Rifles: Ruger 10/22 with 4x Redfield scope, Old Remington Pump .22, Winchester Lever .22, and a crossman 1377 pellet pistol.
Now, if I'm in an area where I'd prefer a shotgun, the .410 wins. It's got full chokes and carries just ever so sweetly. Plus, it was my grandfather's who has since passed away, so that makes it even sweeter.
If I'm heading somewhere where I want a rifle, I love to take that Winchester Lever action. It's got a little more heft (weight) to it that makes it balance just right. Problem is, it's not mine. It's my Aunt's and gets used at her house to keep the grey sqirrels out of the bird feeder. I'm free to borrow it anytime though, and lately I've been taking it out on loan for most of winter break. This rifle carries nicely, shoulders nicely, and shoots nicely.
The old Remington pump (not sure of model) is also a sweet little rifle to carry, even better than the Winchester. That's because it's so tiny, I can wrap my whole hand around the reciever. It's accurate too, but I shoot the Winchester better because of it's heavier.
One thing I have to say, is that I prefer to carry my rifles/shotguns. I like something that you can cradle in your arm or carry in your hand, not something you have to sling over your shoulder. Plus, I've developed a fondness for some of the older stuff, cause generally it had better contours. That's one of the reasons I don't like the Ruger 10/22; it has a square-ish stock and just doesn't carry as comfortable or feel as good in my hands. The other reason I don't care for it, is because it's scoped. Nothing wrong with scopes mind you, but my eyesight's good enough that I don't need them and they make carrying the rifle less comfortable. Both the Winchester and Remington have very fine sights with a fine brass bead front sight. I LOVE those brass bead front sights. And these are tiny on both guns, allowing for some precise shooting.
One other firearm that I have shot, but never taken a squirrel with is my buddy's game gun. It's a break action .22 over .410 that was his fathers when he was a kid. It balances nicely, carries nicely, and is a tack driver. I'd love to have it and if I did, it might just rank as my favorite. Only reason I've never shot a squirrel with it is my buddy won't give it up, even for a moment while he's in the woods. Can't say as I blame him though.
One interesting note for some, is that this coming squirrel season I'll be trying out some new firearms. One is a Ruger Super Single Six and the other is a S&W K-22 Masterpiece (also belonged to my grandfather). I live in NYS and my pistol permit was issued just last week. I also plan to start bowhunting squirrels sometime in the future.
So, what was your question? Oh yeah, my favorite...
If I had to choose, I'd say it was that lever action Winchester, with a very close second going to the Remington.
As for ammunition, I shoot the cheapest bricks of .22 I can buy. Usually Federal or Remington. I also do all of my squirrel shooting off hand, and can't say that the extra cost of CCI mini-mags is justified for me. However, I will say that I did buy 50 of them once, just for the plastic case they come in. It makes a handy dispenser of ammo and you can drop out exactly how many you need at one time.
For shotgun ammo, I only have to say...High brass, baby. High brass. :wink: