If you only count CL floor as upgrades then my strike rate is pretty poor. In 2010 I think I ended up with about half a dozen suites but only 1 CL!!!

My experience is thus that suites are more prevalent as upgrades, but in reality in my view I am almost always upgraded, single to double, double to queen, queen to king, larger rooms, corner rooms...

As always, YMMV, but perceiving upgrades by CL floor is pretty single dimensional. I prefer nicer rooms with more character rather than a souless box close to the CL.