Major carriers on the EAU→SJU corridors in January typically include American Airlines (via Chicago O'Hare (ORD) or Charlotte (CLT)), Delta Air Lines (via Minneapolis–Saint Paul (MSP) or Detroit (DTW)), United Airlines (via Chicago or Newark (EWR)), and JetBlue (on final legs from NYC/BOS/MCO to SJU). American often provides strong network connections and frequent SJU service from ORD/MIA, Delta offers reliable winter operations through MSP/DTW, United can be competitive via EWR or ORD, and JetBlue provides comfortable transcontinental service into San Juan from Northeast hubs. For baggage allowance, onboard comfort, and loyalty perks, compare base fares versus bundled fares (Main Cabin vs Basic Economy). If comfort and legroom are priorities, consider upgrades or carriers with premium economy or extra legroom seats on the long-haul segment. CTA: Compare itineraries across multiple airlines, factoring total travel time, baggage rules, and frequent flyer benefits to choose the right January flight.