This question for me all depends on what I am doing and where I am going. In this order is what or how I carry.
Everyday in town use - Para Warthog .45 acp with frangible ammo, as a back up on a chain around my neck I have a North American Arms (NAA) .22lr mini rev 1 1/8" barrel with CCI Stingers. Sometimes I will use the folding pistol grip holster. Note: NAA will add a chain holder on the NAA Mini Rev, just have to send it in for the work
Close to home walks - NAA Guardian .32 with glaser safety ammo in a pocket holster, NAA mini rev on a chain around my neck.
In the car (Ohio requires that the firearm must be visable w/o search and in plain sight). I Use the Para Warthog .45 in a special cup holder Hi Rise holster I invented with the clip having a bright orange polymer bumper for plain sight visability.
I carry many different and at different times back up pieces when on duty, The NAA Mini Rev, Hi Standard Derringer in .22lr, Colt's 1962 .32 acp Pen Gun (single shot and last ditch weapon, but truly looks like a pen in my pocket), I even have a Stinger Knife/Pistol combo, looks like a standard folder knife like a camp knife but has a .22lr single shot barrel as one of the blades. I got it to work really well with some tlc and fine tuning, now in a last ditch I would trust it. I will also at times carry a Beretta Mod21 in .22lr.
The smallest automatic I would trust my life with is the Guardian .32 made by NAA. Over the years I have had the chance to shoot many pieces, many I consider junk guns like the Kahr's, Sterlings, Ravens, New Charters, Jennings, AMT's, Bersa's and that whole line of unreliable pieces. The older Charter .44 Bulldog once smithed for a trigger job was a fine carry piece in town.
I am not a true fan of any of the Glocks, but have shot them and they work.
A Colt Pony in .380 is a nice piece, but truly needs smithed to work right for save your life work. It is very rough out of the box.
in the end... if I grabbed just one piece to carry running out the door, it would be the Para Warthog in .45 with two extra clips in a very well made shoulder rig or back pant holster. It is a little beast that will chamber damn near anything and very very very reliable. I have over 2000 rounds through mine and with a slight clean up, still looks and shoots like new. I did make one change in that I added finger extensions on the clips as it has a tendancy to lose your little finger under the mag w/o it. I sent it to Para for a 2000 round check up, they said good to go as is for the next 2000 with no adjustments or spring replacements.