Just mail it with regular service. You can do expedited if you feel like spending extra money for no particular reason.
The service times they list on the State Dept website are definitely a case of "underpromise and over deliver". When I renewed mine a few months ago it said standard service was 8-12 weeks but I got my new passport in 4 weeks.
There's an existing thread if you feel like reading peoples' recent experiences.
Current US passport wait? (Merged Threads)