Well, in the current team? Yes, he was the best, but there are others as well, who have done reasonably OK as well like Masakadza, Brenadan Taylor, Prosper Utseya etc. If you say all-time, Andy Flower wins hands down.
True, there are quite a few who would fall in the good category - maybe, not great, but good, yes - Campbell, Grant Flower, Houghton, Paul Strang, even guys like Guy Whittal, Neil Johnson etc. If I had to name the best, it would be Andy Flower.