Purely a matter of choice - my preference is for 6x12 and 135
mm, with 210 and 360 also used often. My personal feeling is
that a combination of 6x17 and 90 mm makes it very hard to get a
close-up of anything without falling over yourself or getting
your shadow in the picture! I have a Nikon 135/5.6 Nikkor-W,
have been very pleased with it.  As regards a recommended
system, I would say any regular 4x5" camera with either a 6x12
holder or a step-up back and 6x17 - can't quite see the point of
enormously expensive panoramic cameras when any other camera can
do the same job!