I think it depends alot on the carriers lifestyle & hobbles...
that said... "most of mine have straps... but then I've been known to ride ATV's agressively, work around on the farm, etc...
when I 1st started carrying, I had my S&W snubbie fall out of a cheap Uncle Mikes holster, like 3 times ( 3 strikes ) I threw away the holster, & had a baddly scratched up revolver
... so now I have both revolver & auto holsters both with & without straps, & wear what works best for what I'm doing that day, I think all my holsters are leather... & I don't think you could give me a nylon holster after my initial expirience with that Uncle Mikes holster
BTW... I also make holsters... & one of my favorite revolver retention systems is the "cylinder window" which I had seen on some vintage holsters... my favorite was custom made for a custom old S&W top break single action snubbie, & the revolver "snaps" into the window, & yet draws nicely as well...