Personally, I like the Sundstrand. Mine has been great, but I realize that I have been both lucky and maybe well suited for it. I live in a fairly cool climate (Pacific Northwest) without a lot of humidity, and I have a Keith Freon system in my airplane. So my Sundstrand has a pretty easy life compared to one, say, based in Florida or Louisiana or somewhere.
I am also religious about adding oil at 25 hours (per the AFM) and never, ever, ever, ever, ever using Max Flo.
Have you gotten yours overhauled, or did you buy a used one? If it was overhauled, who did it?
If you want to give up on the Sundstrand then Enviro is the only real choice.