Crown Molding and baseboards don't have to exactly match to give a good look.
But if you can get the baseboards and crown molding to match as best as possible the look will be more appealing.
You should also match the size of the baseboards with the crown molding so they should be in similar heights to each other to give an appealing look when installed.
So if you have taller baseboards then go with larger crown molding to get the best look.