I was listening to Dominic Sandbrook the other day (from "The Rest is History" podcast). His point was that if you had to pick any empire through history to live in (without knowing your place in it - a sort of Rawlsian Veil), you would probably pick the British Empire. It wasn't perfect, but more benevolent than a lot of other empires.

I would choose the Byzantine Empire but I'm biased. But you can tell based on my romanticizing , British Empire gets the silver.