Based on players who actually played a few matches for us and came with big boots to fill, high expectations or spectacular transfer fee. In my opinion that excludes the likes of Taibi and Prunier. Bosnich did for instance take over from Schmeichel, and failed spectacularly.
Bosnich
Darmian - Jones - Rojo - Buttner
Poborsky - Veron - Kleberson - Depay
Sanchez - Falcao - Di Maria
We've had a few interim GKs, the period between Schmeich and VdS was our worst. I think Bosnich was the worst of the lot, the rest (except Taibi) had decent runs. I think the back four issues have been something of a post SAF thing, we almost always had a great back four under SAF, while we've failed to replace any of those guys after his departure. The midfield and strikers has been our worst area in my opinion, it's almost impossible to pick among all the mediocre candidates over the years. I'm pretty happy with my mid four, all had high expectations when they arrived. Pob and Kleb came from success in international competitions, Veron was an established and expensive world beater, and Depay was assumingly a great prospect. The strikers cost a shitload, even Falcao's loan was expensive wasn't it?
Other good candidates would be Jordi, Djemba, Miller (the next Keane), Anderson, Bebe, Zaha as well as 90% of our signings post SAF. I'd even throw Pogba in with the lot. It's only with Ole we seem to have started to actually apply a strategy.