I find the MB & Diamonds sound allmost the same. They're bright in the high frequencies. The Bostons are more neutral throught the entire frequency range. If you listen for extended periods of time (long drives) the Bostons might be easier on your ears.
i would say the bostons unless you wanna be a tweeter king...never heard a set of diamonds or quarts (owned all 3) that i could listen too for more than 5 minutes that wasnt rta'd and then eq'd so it didnt "break glass". the people that do well with these components (diamond and mb) take the harshness out.....thats why you have bostons and focal and dynaudio and image dynamics...heck even the jl sets lol. they are more mellow from the word go.....Oz audio is good also