What will you use it for? A yoke ST1 was my very first reg, and while I still use the 1st stage on my single tank rig I've since sold the 2nd stage. Notably, it has never been serviced and still puts out the same IP it did shortly after I bought it. One of these years it may start creeping, but it's more likely I'll service it at the 5 year mark just because.
As a recreational reg that will probably outlast you without ever corroding or having the EAN limitations associated with Titanium, it's hard to beat the ST1 just the way it is. As a technical reg, it's not a great choice unless you're getting a different 2nd stage and a monel piston upgrade in the 1st stage. On the plus side, it will breathe great and is backed by Atomic. OTOH, you simply won't be able to tell the difference between performance levels of an Atomic piston versus a lower quality diaphram within recreational diving depths, and even if you could the dirt cheap Z2 or Z3 breathe the same as the ST1. SS is more durable than chromed brass, but chromed brass is plenty durable.
If you're doing serious cold water diving(ice diving, not NE Atlantic in the winter diving), or you want to eliminate the service costs associated with sealing piston regs, you should look at diaphram regs like HOG or Apeks. Personally, I think Apeks are better built but Hog has excellent customer service. Take your pick.