Delta: As an ATL hub carrier, Delta often offers multiple nonstop flights from Hartsfield-Jackson Atlanta International Airport (ATL) to San Diego International Airport (SAN) with reliable schedule options and premium cabin upgrades; checked baggage and seat selection fees vary by fare class. Southwest: Known for competitive pricing and two free checked bags, Southwest frequently provides value nonstop service on ATL–SAN, especially for budget-conscious January travelers. American: May offer fewer direct options and more one-stop itineraries via Phoenix or Charlotte; good for AAdvantage members or specific connection needs. Choose Delta for schedule frequency and elite benefits, Southwest for low fees and baggage policy, and American if your itinerary aligns with their hub connections. CTA: Compare January fares and baggage rules across Delta, Southwest, and American to pick the best airline for your ATL to SAN trip.