I think the answer to your question would be whatever is comfortable to you and eases your mind when you step out of the house. It also depends on where you are going, but not much. If I knew I was going to the bad side of town, I would tend to carry something a little more approriate. But bad things can happen anywhere these days. We should always carry the best possible service handgun for protection. But that is not always possible. I prefer to carry a full size 1911 and at least two spare mags. But somedays where I live, the temp reaches the high 90's and the humidity is enough to take your breath away. Shorts and a t-shirt or polo shirt is common place. Sometimes you have to go smaller. I routinely have a S&W Airlite Ti snubby in a Kramer pocket holster. If I can wear an untucked shirt I carry a Glock 26 in a Pocket holster, with the shirt covering the bulge in the pocket, or a waistband holster under the shirt in the appendix position just foward of the hip.
I still carry a full size gun when ever possible or dressed with enough clothing to cover it. But sometimes adjustments have to be made from time to time. The smallest gun that I have carried in recent memory was a Walter PPK. I have a Ruger LCP and a Kel-Tec P3AT, but it's very hard for me to shoot them with my large hands. Even though it's so light, it's like carrying my car keys, I just can't shoot them well enough to carry for defense. So I opt up. I do own a little Beretta 950 in 25 ACP, but it never gets carried except for back-up or hide out gun, in addition to my main carry.
Some people feel under gunned or out gunned when they carry a J Frame snubby, but I practice with mine regularly and feel confident with it. You'd be surprised at the people who have fought their way through a gunfight with a 38 snubby, while the other guy had a hi-cap pistol or rifle. No, it's not the ultimate gun, but it depends on the person standing behind that gun, his tactics and skill.