Ouch, difficult as I have loved one (or more) from almost every top five...
I adore Pride and Prejudice, but it gets edged out by Persuasion, just.
My favourite Daphne du Maurier is House on the Strand.
Robertson Davies would be up there, but not sure which one novel I'd pick...possibly A Cunning Man.
John le Carre... probably The Little Drummer Girl
From my childhood favourites, the first time-slip novel I loved would be A Traveller in Time, by Alison Uttley, which was 50 years old when I read it and still comes up fresh as new paint. Very pleased to see James Long's Ferney on this selection: I enjoyed that, and thought I was the only person to have read it.
This is the most impossible of short list tasks... tomorrow's list would be quite different.