It's worth looking for package (Eurostar + Hotel) deals, as I've often managed to get these for less than cost of the ticket alone! Try here and here.

Otherwise, these days, the only flight I'd consider is the very convenient LCY-ORY on AF. Door-to-door time tends to be less than the train on this for me (LCY has a 10-15 minute check-in time for AF). But that tends to be rather expensive (not to mention that LCY is closed Sat PM and Sun AM).