I have only one 35mm and one medium format camera. I would like to shoot Delta 100 or Fuji Acros 100 in the FM2 since I don't like too much grain, but for what I use the Nikon for (indoor/lowlight) I am usually in need of more speed so I have just bought some Delta 400 to try and I hope that does the trick. I find Tri X and HP5 are too grainy in 35mm. If so I will stick to just Delta 400 for b/w.
I have two backs for the RB67 so I usually keep Delta 100/Fuji Acros 100 in one and then Tri-X/HP5 in the other. I find the grain is not much of an issue on 6x7 negs.
I have only ever shot colour on Portra 400 in the RB67 and was blown away by the lack of grain. So Portra 400 or Portra 160 (depending on lighting) would be my colour film of choice. It would probably make more sense to get an ND filter and just use Portra 400 for all colour stuff now that I think about it.