which is the best wood for a patio set?
Redwood, cedar, and teak are probably the most common rot-resistant species used for outdoor furniture. The first two are a pleasure to work with, but they're very soft. That means that they can be damaged more easily. Teak tends to be less common and/or more expensive. 

Pine (or spruce or fir) is inexpensive and can actually last quite some time if properly sealed and not left in consistently damp environments.