Mil dot and BDC do different things.
At the end of the day, you gotta know something about your round to accurately put the thing on target. Ranging is half the battle, but only half.
If you get a pre-made BDC, be sure to check it for accuracy at all ranges needed. You can't buy one, zero at 100, spin up to 600, and expect to be dead nuts - it ain't that simple.
If you really want a good BDC, make your own data tables and send the data to Kenton, he'll put your data on a turret for your scope. The pre-made BDC's can be very close, but nothing beats real-world numbers.
And finally, ranging is a very perishable skill, a Mil dot will help, you you still have to do your part.