For me it has to be fast lens, as I love isolating my subjects... and dislike grain in colour shots
F 1.7 on my Oly Sp and Yashica GTN
F 1.4 on my Pentax 50mm (SLR)
Although I need to work on my focus, just got some SLR pics back and in quite a few the focus was off a bit (mostly indoor daylight ) at F1.4 and a fast shutter speed.
My favourite combo w/ my SLR is 1/2000 and F1.4!
Which makes me want even more an R3 with the 40mm F1.4...
Maybe one day I can justify it!
-Nick