I've been to many places where the Doubletree has been cheaper than the Hampton. In Boston, I can often get the Doubletree Suites for under $120 if I book far enough in advance. The Hampton Cambridge, meanwhile, is often $129+.

In general, the rack rate for the Doubletree is higher, but they discount more aggressively during the week. Hampton sets its price, discounts it 10% for some groups, and that's about it.