In my opinion it's Marcelo Bielsa - a tactical genius, who has found praise from the likes of SAF and Guardiola. His Athletic Bilbao managed to stifle Guardiola's high flying boys into a draw in a La Liga. He managed to beat SAF's Man Utd in a match at Old Trafford (Manchester United 2-3 Athletic Bilbao: United unable to deal with pressing and high tempo). The only trouble with him is that his teams seem to be unable to keep up that level of energy sapping performance consistently. An excellent article on him - Who is Marcelo Bielsa, the fabled manager who could join Swansea City? He doesn't have the silverware to show off, but his genius hasn't gone unnoticed totally.