I am on an Intel Mac. I tried Mixmeister on the PC side but there's a bug between it and iTunes. Tangerine does not seem very accurate. Dekstasy seems very impressive functionally, but not very easy to use. Beatunes does an OK job with the accuracy turned all the way up and the proper beat range selected. In general one has often have to halve or double the BPM a tool comes up with.
I am finding that if one measures every song by quarter note as the computer does, the results are often misleading. Two songs can have the same BPM and yet one feels half as fast because it only really emphasizes every other note. In these cases I have halved the measured BPM even though technically it was probably accurate.