The Dartmouth Arms does a great roast and the signal great too (kids roast a bargain for older kids).
My parents in law really liked the roast at The Hill. Not top of my list but fine and very good value. The Railway Telegraph also reasonable (but I think has recently changed hands?).
Not tried the roast at The Sylvan Post or the Perry vale (but other food at Perry Vale very good).
Further a field the Rosendale in West Dulwich is fab. The Herne good but not been so recently.
I am super fussy about pub roast dinners and ideally like rare roast beef. The husband can't stand reheated meat and I have kids that love roast but hate gravy. Yorkshire pudding is a must have in my book. Good luck!