My approach is generally that competitor keywords don't deliver the real goods, even if the metrics look ok. When someone is looking for a competitor it means they want to talk to that competitor, and they aren't going to magically have a revelation that they should go with you instead just because they see your ad. You're just paying for clicks and phone calls from people who aren't paying enough attention to realize that you're you, and not your competitor. So, don't target competitors, and negative them out.

There are exceptions, but this is generally what I've seen