Its all personal preference -
There is no medical documentation saying that Cropped ears get more or less infections, mite etc and vice versa with floppy ears. A majority of this relies on the owner and how clean they keep the ears and what environmental aspect they are exposed to.
Of course a cropped boxer playing in the dirt will get their ear a bit more messy than a natural eared dog, however, I know my two natural eared dogs always get their ears flipped up when they are playing or running around, so put them right back up there with the cropped.
I love the cropped ears when done by an experienced vet. Jill (Jinxx's ) Zorita is my cropped ear model. We went to the ABC last year not being fans of the cropped ear on a boxer. Mainly due to the fact that around our area there are some pretty bad crops. However, when you are in a room, with boxers who have them done by experienced vets, there is something so striking about it, that it literally changed our view on the crop.
Second ear leather plays a big part in it as well. If you look at a majory of the Euro dogs their crops are a bit different than the NA lines. They are cropped shorter due to ear leather. If they were cropped like the NA lines, they would not stand as well. NA lines have more leather so they crop real nice (when done right, by an experienced vet). Many NA lined dogs who show natural, need to have a good ear leather and proper care (taping, massaging) so they lay correct.
Other dogs in the US ring that are showing naturally are UK, or crosses who have great ear leather and look fab natural.
So to me, its personal preference. If I get a NA line dog, it will be cropped. My Euros are not. I think the crop is only as good as the person who is doing it as well. So research is key. Go to some shows, look at some dogs who's crops you like (boxer club) and then get referals. I would not suggest going by the cheapest price, but by rep and experience. Its like getting a face lift. You would personally want the best, so you seek them out.