Ear cropping is a personal preference. If you choose to have your puppy's ears cropped, the procedure should be performed by a veterinarian experienced with the proper Boxer ear crop. Having attractive cropped ears is 5% surgery and 95% after-care. However, if the surgery isn't performed correctly, there is no amount of after-care that will help poorly cropped ears.
You should discuss the pros and cons of ear cropping with your breeder. They will help you make an informed decision, direct you to an experienced veterinarian and help you with aftercare and necessary "taping" or "posting" that will train your puppy's ears to stand correctly.
A definite decision must be made before your puppy is 8 weeks old, to allow time to schedule the appointment. Most veterinarians prefer to crop between the ages of 7-10 weeks. After 10 weeks, blood vessels in the ears are too big, and the cartilage is trained to lay flat. Cropping after 10 weeks risks not only a poor crop, but your puppy's life.
Directions on post-operative "ear posting" should reviewed in person, and written instructions sent home with you when you pick your puppy up from the veterinarian. If your vet or breeder can't help you with aftercare and posting, the information is available online. It is strongly recommended that posting instructions be followed, in order to complete the process of beautiful cropped ears.
Below is a link to the chart of veterinarians used by boxer people in the U.S. and Canada.