Finally actually chose a caliber to put in the poll.

I'm sticking with the .22
I really love my big bore and borerifle dobles, the Jules Bury 8x60R BoxlockEjector is the ultra sex machine...

The 22 is something I use almost every day though.
It keeps me fresh and quick shooting fast over the iron sights, I'm doing rapid reloads and getting back on the sights scanning the field, and it's accurate and deadly on a seemingly unextinguishable, neverending population of aggressive urban (downtown oakland!) varmints.
The little double keeps me 'on it' year round.

Furthermore, there's zero recoil and zero muzzle report with my preferred ammunition, the CCI CB long.
My daily practice is nearly free in respect to ammo cost, and there's no sight/sound to bother the neighbors.
I can even shoot it inside the house (I have a good 50 foot 'range' inside the house I can use when the wife/kids are gone and 40' indoor in my machineshop behind the house.)

Last/not least is possibly the neatest feature of all.
My children will be learning to shoot over the iron sights of a SxS double!!

--Tinker