I have used Heine in one exam room, WA in another, and I have a Keeler. I have not had a problem getting a view with any of them. Several of the people in my class who got WA have had problems with them. I'm not sure what, but they did have to send them in.
The Keeler is very nice, the teaching mirror can be flipped in place or flipped out of the way if you are having trouble with it. The other brands are a little more difficult to take on and off. I have been told Heine has a good battery life, but I have not really had a problem with the life of my Keeler.
Just like the diagnostic set, get the one that fits you best.