I have alloy frame sigs in 239 models ....and stainless in 226 models...and there is a little more wear showing on the alloy frames....but I don't think its significant.
I am typically biased toward steel frames ...and more toward polished stainless than blued steel...because I like the look better...
I have a pair of all polished stainless 226's ...one in .40S&W and one in 9mm ...and they're great guns / not my primary guns ...but they probably have 5,000 - 10,000 rds thru them, not a lot, but enough to see a little bit of wear...my 239's ( one in 9mm and one in .40S&W as well ) have maybe 5,000 - 10,000 rds thru them as well ...mostly with the grandkids ...and while there are scratches on the rails on the frame...nothing deep and nothing significant...and I primarily use CLP Break Free...and its heavy enough vs grease on the rails in my view.