luton, gatwick or stansted airport??
 

I am going to book a flight from nice to london via easy jet- I have a choice of these 3 airports to fly into. Will want to get to Windsor after landing. Which airport is easiest to navigate, get to Windsor from etc.??

No way that you can book a flight into Heathrow is there? That's very convenient to Windsor (bus or a 15 minute taxi ride). The other airports, not so easy...in a pinch, choose Gatwick and take the National Express coach connector to Heathrow (about 1 hr 15 minutes).

No-Heathrow's not one of the choices listed.Is the bus you mentioned something you should book in advance or day of purchase?

Does it have to be EasyJet? BA flies from Heathrow to Nice, and it would be markedly less hassle. Heck, I would even consider a sub-1.5 hour connection in Amsterdam or Paris.

You don't need to pre-reserve the bus.

Out of those 3 I'd probably pick LGW (Gatwick).

There are frequent trains from Gatwick to Clapham Junction and from Clapham Junction to Windsor. The total journey time is about an hour and a half.