I use 35mm in 95% of time. Print up to 30x45cm. When I want grainless results (rarely) I use ISO 20-100, but most of the time I use iso 400 films and I like the grain. Actually grain is the last thing in my concern - most important is composition, meaning... when I make something that I like - I never think: "ohh if only I had used medium format or lower iso so that grain is not there". Actually often I use Lith print to get grain bigger (Moersch Easy Lith + Fomabrom is the key example: http://darkosaric.deviantart.com/art/Lith-10-130219602 ).