I'd have added RDM but not sure how responsible he was for the signings made, I doubt he had much of a say. For me it was a no brained, Gullit. Given his budget was lower than that of Vialli, Ranieri, Mourinho and Carlo he did extremely well in the market, bargain buys like Zola and Flo, then of course RDM, where would we be without him?
The majority of Ranieris buys were pretty much a success or good tbh. Never really rated him as a manager though unfortunately, was good but wasn't great. Good eye for talent / buys though. All his £££ buys : Lampard, Gallas, Gronkjaer , Petit, Zenden, G.Johnson, Geremi, Duff, Bridge, Oliveria Veron, Cole, Mutu, Crespo, Makelele, Parker, Cech, Robben, Ferreria
Mourinhos were not that great tbh, the majority were poor overall, but lucky he was an amazing manager !! All his £££ buys Jarosik, Carvahlo, Drogba, Tiago, Kezman, Mikel, Shevchenko, Kalou, Essien, Wright-Phillips, Diarra, Del Horno, Ashley Cole, Bhoulrouz, Malouda
Gullits £££ buys Zola, Babayaro, Granville, De Goey, Poyet,Flo, Le Saux, Ferrer, Casiraghi A lot of good ones there
Hoddles buys Minto, Furlong, Stein,Peacock, Kjeldberg, Hughes, Gullit, Rocastle, Lebeouf, Di Matteo, Vialli, Petrescu Some good buys there as well
I don't think you should judge a manager on his buys, since most managers don't have long enough to build their own squad, and have to work with the majority of the players of the manager before them (who generally is considered to have failed). Also, managers like Hoddle simply never had the money to spend that his successors have had.