Like any hobby, this part can sometimes take over! I tend to take the M7 everywhere and reserve the Minolta600 for certain duties like telephoto, macro or low light work where I use TMAX 3200 pushed 2 stops to ISO25000.
In general, my philosophy was to go to medium format to achieve higher quality in terms of tonal range and resolution. Therefore, size was everything and so I dismissed the 6x4.5 cameras and went straight to 6x7. I am mostly interested in landscape therefore 6x6 was not so suitable (although I'm sure Charlie Waite would argue with me there) and I could always crop down to 6x6. This left very few to choose from. Right now if I had to buy a single medium format camera again, it would be a close call between my Mamiya7 and a Pentax67. The Mamiya wins hands down for compactness, hand-holdable, fab 43mm lens and quiet. The pentax scores with graduated filters, close-up accessories and larger lens range. I can still see me getting the Pentax one day but the Mamiya is a beauty. I bought the RZ67 simply to get a camera more suitable for studio work. Its an SLR, has removable/rotatable backs and is very robust, but it weighs a ton. Then there's large format! I am looking at these at the moment, checkout the work of Joe Cornish, Fatali. Large format is not as expensive as you might think, but it is a whole new way to photograph.
For B&W work I exclusively use Kodak TMAX, either100 or 3200 depending on what I doing. I have dabbled with Kodak High speed Infra Red (HIR) using a red filter, but I have had limited success.
For colour, I use Fuji Velvia. I have tried Kodak's Vivid Extra Colour 100 and quite like it, but Velvia (or Vulvia as John Christian termed it!) is magical. I was on a Light & Land course with Charlie Waite who said "don't press the shutter unless you can see the picture hanging on your wall. Nothing magical will happen between now and the picture coming back from the Lab". Well, with Velvia I have to disagree. It never ceases to amaze me how often images seem "better" than they seemed, especially in low contrast conditions.