The Servant and Accident were real classics.
The Servant was menacing in a slow insidious way, Dirk Bogarde (trying to break out of his film-idol mode- his previous film was Doctor in Distress) and James Fox were a good pairing. The novel by Robin Maugham (related to W Somerset Maugham) is worth reading.
The bit I liked most in Accident was the restaurant scene, scatterings of dialogue from each table as the camera bobs in and out.
I can't remember much of Go-Between and am not sure if I have seen Butley, so need to add them to my rental list.
Pinter has scripted a wide range of films, as well as his own work, including The Quiller Memorandum, The Handmaids Tail, The Comfort of Strangers and he has acted in an equally broad range of cameos (Rogue Male, Wit, Breaking the Code).
The best film of his own work (I think) is the early Caretaker with Alan Bates (as you say, always great), Donald Pleasance and Robert Shaw. Each actor totally captures the role and they bring out the humour as well as the darker side.