Due to termite damage, I need to replace a rim joist that supports the front wall that has a sliding door. It is a 2x6 beam that goes across the room. I want to make sure that the best material is used, e.g.. oak, cedar, pine, redwood.

Pressure treated lumber would be the most resistant to any further infestation. Be sure to get a piece that is straight and true. Install with crown up.

Chuck