For bumpy roads, a larger wheel is better, and you have the most tire choices in 700c. I think the lower Crr you may get with large wheels is overemphasized though. What is more important is how the bike's ergonomics work with you and what you want to bike to do. Big front wheel = high bottom bracket. Are you comfortable with that for what you want to use the bike for? I have both and it's horses for courses.