Not realizing how cheap car rentals were, we opted for the airport shuttle.
On the downside, we were pitched a timeshare offer by the guy who sold the tickets, had to wait for the shuttle to fill up with pax (about 15 minutes), and stopped at a few other hotels before we got to the Westin.
On the up side, it was cheaper than a taxi, and the Westin is on the east end of the hotel corridor which is closer to SJD so you would be among the first few stops.