Overall I would give ST a C.
I was a NW Gold and am now FB Gold. I generally fly between the US/Europe/and Asia

I stay with them since I often fly NW(RIP), KL, and AF. I can only compare to *Alliance since I'm also BD Gold and have also flown LH/OS/SQ.

Pros
-Good transatlantic/northern asia coverage fitting my travel pattern
-African presence
-US Domestic upgrades (even for FB elites on NW)
-Lounge access for Elite Plus
-NW (maybe DL to a lesser exent) had many mile earning promotions
-FB 50% promo awards/NW(RIP) intra-Asia awards
-FB possibility to earn status with Amex
-Addition of new members such as Aeroflot/Vietnam Airlines (additional destinations)
-Competitive pricing


Cons
-Poor coverage of Southern Hemisphere/Middle East/India
-Poor RTW offer due to the above point
-no outstanding 5* member
-rather average/poor service/product
-difficulty redeeming awards (FB/DL)
-few alliance wide promotions
-few alliance wide benefits except for lounge access and maybe priority boarding/check-in
-Losing Continental/Copa