It's all about fit. I had a pair of Sidis for about 7 years..thought the fit was good until I bought a pair of Specialized at the end of the summer.
Try on a lot of shoes. If they don't feel good off the bike, they won't feel good on the bike. Also, don't do the silly thing of putting on a pair and walking around the fitting area. Bike shoes are made for pedaling, not walking.