A good reg from a reputable company will do the job.
Personally, I like Scubapro based on 20 plus years of diving with them, and from a regulator technician perspective, I like they way they are designed and the general ease of service.
My preferred back gas first stage is the Mk 17 due to excellent performance, it's well executed sealed design and the clean hose routing possible when used on doubles. It is also in my opinion the most bullet proof cold water first stages around at this point.
For deco purposes a simple unbalanced piston design like the Scubapro Mk 2 is hard to beat. It is by design perfect for high O2 applications as no part of the reg past the HP orifice is exposed to more than intermediate pressure and there is very little upstream of the HP orifice. The design also provides ample warning of low tank pressures and when paired with an adjustable second stage like the G250, offers excellent breathing performance.
The G250 is hard to beat for a second stage in any application as it is a well proven and excellent performing regulator.
With SP you can also order any first stage with any second stage through your local dealer to enabel you to customize the reg to yur specific needs. You lose a few percent on the package discount but you don't get forced into buying more first or second stage than you need in a specific application.
I agree with the sentiment that interchangeability is important. I go one step farther and set up all of my first stages with the same IP so that any second stage can be quickly attached to any first stage with no need for adjustment.
