CREATE TABLE table_203_515 (id DECIMAL, "rank" DECIMAL, "city" TEXT, "passengers" DECIMAL, "ranking" DECIMAL, "airline" TEXT)

was los angeles or houston the busiest international route at manzanillo international airport in 2013 ?
SELECT "city" FROM table_203_515 WHERE "city" IN ('los angeles', 'houston') ORDER BY "passengers" DESC LIMIT 1
SELECT "city" FROM "table_203_515" WHERE "city" IN ('los angeles', 'houston') ORDER BY "passengers" DESC NULLS LAST LIMIT 1