London Gatwick and London Luton also offer a few flights to Edinburgh but have longer conformance times and are way further from the city (so there's no point flying from them if you're inside London, the train is faster).

And even worse for Stansted: the Stansted Express, the fastest route available between Stansted Airport and Central London, takes 47 minutes from Liverpool Street.

Flying though London Heathrow will take even more time (to get there: 15 min train from Paddington station every 15 min, and because the minimum conformance times are higher). So this will probably bring you closer to 3 hours total, city center to city center. time waiting in the boarding room or for check-in ( 15 to 30 min at least, depending on whether you have luggage or not).

traveling times to the airports: London City Airport is close to the city center ( 22 min to Bank Station), but Edinburgh Airport is not ( 35 min by the tram or 30 min by the slightly faster Airport 100 bus, or 25 min in light traffic if you're driving or taking a cab outside peak hours) – add also some waiting and walking time.

Flying is the fastest option (1h10), but you'll have to take into account:

London city airport to edinburgh