My experience has been that many folks don't like selective color images especially well. I have to admit I'm not a fan of the technique. Occassionally one will strike me but certainly not frequently. Usually for them to work there needs to be some serious color pop included in the image. The grebe comes the closest for me due to the red eye and bright yellow bill. Of the choices the Bald Eagle would be my second choice, followed by the train.

I'd be curious to hear how they sell at the end of your season. Simple curiousity. There's a few places close-by me that would like post cards but I'll be darned if I can find a source where I can purchase them and still make a buck selling them wholesale... at least without buying a huge quantity.