I'm not sure what you mean by "downtown," which has a different meaning in New York than in most cities. If you're coming from DEN on UA, you have 2 choices on a nonstop: LGA and EWR. If you want to take a taxi, LGA will be cheaper. If you want to take public transportation, EWR is better. What facilities are you looking for at the airport? There's a better restaurant at LGA below the UA gates than any in the UA terminal at EWR, but are you really planning to eat there? LGA is more prone to weather and air traffic delays than EWR, but all 3 NYC airports suffer from them.