We recommend flying into San Diego or Los Angeles, both of which are international airports.
San Marcos is technically part of San Diego but it's about a 45 minute drive northeast from the airport in Downtown San Diego.
SAN diego airport
Airport Code: SAN
From here, you can rent a car or grab an Uber to your hotel.
los angeles airport
Airport Code: LAX
You can rent a car and drive the 2-4 hours to San Diego or take the train from Union Station (near LAX) to San Diego.