If you're patient and a good loser, then go with the ear that best suits the head.
Uncropped ears are still 'new' and unfamiliar to many judges, and do dramatically alter the appearance of the dog, so some judges may be hesitant to award them. Other judges, of course, will be more than willing to award an uncropped dog if the other qualities are there. As more uncropped dogs are shown, more uncropped dogs will win - but at this point, they're still in the minority, and so may lose even if they deserve to win more often than a cropped dog would (though it happens sometimes to cropped dogs, too).
If you're the kind of person who will have a hard time waiting 3-4 years for your dog to finish, or if you're likely to take your puppy's losses personally (and those types are not at all unusual in the dog show world - people invest their heart and soul in their dogs, and it's hard to see them lose), you might be better off with a cropped pup. You'll still win more than you'll lose (and with some lines it may still take 3-4 years to finish), but probably at a lower ratio, and at least you won't be tempted to blame all the losses on the ears, regardless of the quality of other dogs in the ring.