Its not really a either or type question/answer. There are going to be a number of factors that will affect things.
What do you do for a living, how much do you sweat, what are you carrying the gun in, how much you actually carry it.
If you work in an environment where you arent very active, and things are temp controlled, where you arent likely to sweat much, the results will be very different, than if youre active, and in a uncontrolled environment.
Holster material and design makes a major difference. Leather is pretty and all, but is usually a poor choice if you sweat a lot and carry IWB. Kydex on the other hand, is impervious to moisture, and very little of the gun is exposed to the body. Its a much better choice, but its still not perfect. When things get hot and steamy, everything still gets hot and steamy at some point.
Ive tried all manner of treatments on a bunch of guns, and the only things that have actually worked, was a new finish. Rub and spray ons are about worthless. You need a finish that is rust/wear resistant. The two Ive had the best results with, have been Tennifer and hard chrome, and Tennifer has been the best.
I carried a blued PPK/S for awhile back in the mid 80's. The bluing didnt hold up very well, and was quickly worn off on the back strap and on the slide where my thumb, finger, and palm would rest when charging it. Pretty soon, those points were down to bare, or barely coated metal, and I was constantly dealing with rust at different levels. I had rust on the blued parts as well, so it really didnt matter.
My epiphany was back in the 90's when kydex first started showing up. I was carrying a blued Colt Combat Commander in a couple of Galco Royal Guards. Id been carrying it about a year, and once summer hit, it began to rust badly. Even with rotating through two holsters every other day or so, they never got to dry out, so the gun was always in a sweat soaked holster, and I was usually soaked in sweat all day to boot, so the gun was always in a bad spot.
The owner at EGW said he could probably get most of the heavy pitting out, and recommended hard chrome instead of rebluing or parking it. I did that, and about the same time, found Blade Tech kydex IWB holsters. From that point on, I had very little rust, and I still have both the gun and that first Blade Tech holster, which is as serviceable today, as it was when I bought it 20 some odd years ago. I went from $75-150 a year for holsters, down to $55 for whats looking to be forever at this point. That in itself, has been a major cost savings.
Now, kydex isnt perfect, but its pretty close. It does wear the guns finish at the contact points. That can vary from make and gun too, depending how things bear in the holster, and how its made.
Another advantage to kydex is, you can clean them easily and regularly, right under the tap in the kitchen sink. You dont get the embedded dirt and junk in the inside, like you do with leather.
Yet another advantage, benefits your body. Kydex just slides across wet skin, and doesnt rub you raw. It also doesnt have chemicals in it, to really turn up the burn.
Leather may seem to be easier on the finish at first blush, but over time, its really not. It contacts more of the gun, and the finish tends to quickly fade or wash out where it does. Cleaning the is about impossible, which just helps accelerate things. As I noted above, leather on wet skin, is abrasive, and quickly rubs you raw, and continues to do it.
