Essentially, the only differences lie in the finish and accessories/stocks that come with them.
ADL is the lowest priced of the three with either a hardwood stock or synthetic stock (blind magazine, no floorplate) and a black oxide finish.
BDL is the classic (not a midgrade.) Nice, walnut stock in a classic profile and blue finish.
CDL is similar in quality to the BDL but in a more modern, slimmer walnut stock and same barrel/action finish. My personal opinion is that the CDL is the "prettiest" of the bunch.
...in a nutshell.