As others have said, it depends on what you want.
I'm also new to the XPan (bought an original XPan-1 in mid-May), but I've been shooting regular 35mm with my Canon 1N for a while. I generally go between Kodak E100VS and Fuji Velvia 100. I recently bought a few rolls of Kodak BW400CN for B&W, but haven't loaded any of it yet.
So far, all I've had processed from the XPan has been E100VS, but I have a roll of Velvia 100 in it now. As soon as that's done, I'll load the B&W.