Seriously though the best flat horse in my opinion was Persian Punch and his wins in the Gold Cup demonstrate why
Erm…. 
Sorry jumps is more my thing 
Persian Punch is still my best horse on the flat, even though he didn’t win at Royal Ascot. One who did win at Royal Ascot was FRANKEL and was probably the best miler ever.
You've got to accentuate the positive.
Eliminate the negative.
Latch on to the affirmative.
Don't mess with mister in between.