The answer to "Which film is best for a beginner?" is, it depends (you knew someone had to say that).
If your emphasis is on results, then 400 speed (with the ability to make a photo workable in more conditions than slower film) is a good idea.
If you want to LEARN, then I'd suggest using slide film (at least for the first few rolls). Because slide film does not get printed and tweaked all over the place, what you shoot is what you get, and it's easier for a beginner to tell if the shot is under or over exposed, and where the flash is actually reaching.
And if the MX10 is still the same as when I owned one, it only handles 100 and 400 speed film.
If your emphasis is on results, then 400 speed (with the ability to make a photo workable in more conditions than slower film) is a good idea.
If you want to LEARN, then I'd suggest using slide film (at least for the first few rolls). Because slide film does not get printed and tweaked all over the place, what you shoot is what you get, and it's easier for a beginner to tell if the shot is under or over exposed, and where the flash is actually reaching.
And if the MX10 is still the same as when I owned one, it only handles 100 and 400 speed film.