I've voted here for the Blue Pullman. Never saw one in real life but I dreamt about it as a small boy in the local toy shop window. Now I've got 2 sets and would really like another! To be honest, although I'd pay the £300 or so Hornby would have to charge for a super detail set (2 "locos" £150, 5 coaches @£30 each) I'd be quite happy for a gently revamped 60's toy! 5 pole ring field, flush glazing (which the original Tri-ang ones had anyway), handrails, buffers, lights ... all in a box with that wonderful illustration!! Even as a small boy I could tell the illustrated trains had much more detail than the models ... those were the days!
Hornby's programme in recent years has involved nothing more scientific than going through 30-40 years old catalogues and thinking "we'll do that one"! M7, Brit, A3, King Arthur, class 31, 08 ... well Hornby go back again and settle on the B12!