Cropping vs. Letterboxing for training sets

How are other people dealing with training sets that are landscape images?

• Anyone have luck with just letterboxing? Does transparent letterboxing work?
• Center crop - easy but losing a lot of information...
• Crop left + crop right + crop center - not sure if this would generate too much redundant training images.
• Smart crop - anyone know of a good library for non-face/non-people images?

Just all around curious what others have had success with.