The GWR 3800s sound amazing at full bark, as do the becoppered Castles.
I find Caprotti 5 73129 to be pretty hellfire, too.
On the diesel side of things: 20s, 24s, 25s, 26s, 27s, 31s, 33s, 37s, 40s, 43s (HST P/Cs not Warships), 68s.
I would say that overall I probably love 40s more than any...