the problem is which grass to take into account ? old quick one or modern slow one ? try to make a mixture I guess
considering that, Agassi should clearly be ranked ahead of Ivanisevic, because on quick grass Ivanisevic was a little bit better but on modern grass Agassi would be much better.
The hardest to rank imo is Murray because on old quick grass Murray would have played completely differently : clearly he would have played serve-and-volley, which is a game imo he's perfectly able to play.
I will try to make my rank with this "surfaces mixture" :
Murray, on the quickest of today's courts, loves nothing better than staying away from the net at all costs. See this year at Dubai, although that's not as quick as 90s Wimbledon.