I think to start out you need to pick a film that is going to have good latitude in a variety of lighting and shooting situations. I don't think anything exceeds triX or HP5 for versatility. Then there are the classic developers, D76, HC110 and Rodinol or there equivalents. All three have loads of data and experience behind them, and all three can be used at a variety of dilutions, stand processed, rotary processed and all three provide their own unique look.

Currently I use XTOL for 35mm and HC110 or Pyrocat-HD for LF. And I have a special relationship with PanF and Rodinol. My film of choice most of the time in roll film is Delta 100 or TriX. In LF my choices are FP4 and HP5.

If I was told I could only use one film for all my photography it would probably be TriX.