Heathrow wins overwhelmingly for west London — it IS west London's airport.
Heathrow is the definitive choice for west London. The airport is located in the London Borough of Hillingdon — it IS a west London destination. Paddington is 15 minutes away on the Heathrow Express. Ealing, Hammersmith, Chiswick and Kensington are all within 30–45 minutes by Tube, Elizabeth Line or taxi. No other airport comes close.
For west London, the airport choice is essentially made for you — but here is how the alternatives compare if Heathrow is not available for your route:
Heathrow is physically located in west London. The Piccadilly Line serves Hounslow, Hammersmith, Acton and Ealing directly. The Elizabeth Line serves Hayes, Southall, Ealing, Acton and Paddington. Buses connect the airport to Hillingdon, Uxbridge and surrounding areas. Taxis and rideshares from Heathrow to west London destinations are short and relatively inexpensive (£20–40).
If your route is not served from Heathrow, Gatwick (Gatwick Express to Victoria, then District/Circle Line west) is the next best at ~60–75 minutes total. London City Airport requires crossing central London to reach the west — not ideal. Stansted and Luton are on the wrong side of the city and should be avoided for west London if alternatives exist.
Heathrow is 24km from Paddington. The Heathrow Express takes 15 minutes. Hammersmith is ~25 minutes on the Piccadilly Line. Ealing is ~20 minutes on the Elizabeth Line.
Possible but not ideal. Gatwick Express to Victoria (~30 min), then District/Circle Line west (~20–30 min). Total: 50–70 minutes.