MB Quarts are okay if you go with the QSDs, but you can get comparable for less. The CDT Hign definitions are are about $ 400.00 and they sound just as good. If go with lower priced MB Quart like Premium or Reference series, make sure you attenuate your tweeter by about 4 to 6 dbs or the tweeter will sound harsh.
http://www.woofersetc.com/product.asp?0=239&1=240&3=1171
The MB Quart Qs are very good to use in the back of a convertible though because they have speacers. I could not fit CDTs back there and CDT have a fairly shallow, but wide basket.
I do love the MB Quart QM 25 tweeters though. They cannot be bought in a component set and they are very large (about 1.5 inches).