I like both but prefer the chamois pad that Rapha uses over the high end Castelli pad. Both of the companies make very nice racing level kit, but if you're a muscular or fat body type, the pro level stuff might not fit you.

Rapha often sends people one time use 15% off codes, you can often get a free one if you frequent many cycling forums (somebody will offer theirs up for free if not using).

Past seasons Castelli is often on clearance on eBay and various online retailers. Rapha has a summer and a winter sale. They've quietly seemed to have a year round clearance by listing old stuff under the archive sale section of their website.

People may make fun of the Rapha marketing, but in my experience most if their kit is designed for practical use and well designed to boot. The only big misstep in my opinion is the ballast/internal zippered pocket on their lightweight jersey because it would be more useful to have a third open pocket instead.