Thanks for all your helpful replies.
I think it's going to be the Airport Shuttle.

On the rates page it asks for "provinces" and the options are "Toldas" or "Madrid" - what should I put here and what does Toldas mean?
Am I right in thinking that the "zone" I want is "Madrid Centro;Interior M30; Hoteles"?? (I'm in Hostal Lopez)
Is the fare quoted one way or return?

Eddie,Ive not been to Lisbon but Im very happy to bow to your experience.Madrid is the best of the ones Ive used.Anyway,using any criterion you want-reliability,safety,cost,cleanliness-can we agree tha London is the worst?

Notyor,

The options for provinces are "todas" (all) and Marid.
Yes, the zone you want is "Madrid Centro;Interior M30; Hoteles"

The fare is quoted for one way and they also say at the bottom of their page that "there is a small surcharge over night & holiday services. Our reservation staff will gladly inform you if any of those supplements apply to your service request".