Great, glad it turned up ok.
The games not filling the screen will be integer scaling as far as they can within the available width. You can set them to scale fractionally if you prefer or change the output resolution of the pi to suit. It's very hard to have one setting work perfectly for everything in MAME, there's just too many different things being emulated.
If you put evey rom into each emulator they will show up multiple times in the menu. There is a list of what runs nicely where but it's very incomplete:
https://drive.google.com/open?id=1mgzWFz9rOsjDTKLy0lq_Mab9D1-NrojXRw1yf9GdWoY
with an rpi3 most stuff runs well in any of the emulators really.
The games not filling the screen will be integer scaling as far as they can within the available width. You can set them to scale fractionally if you prefer or change the output resolution of the pi to suit. It's very hard to have one setting work perfectly for everything in MAME, there's just too many different things being emulated.
If you put evey rom into each emulator they will show up multiple times in the menu. There is a list of what runs nicely where but it's very incomplete:
https://drive.google.com/open?id=1mgzWFz9rOsjDTKLy0lq_Mab9D1-NrojXRw1yf9GdWoY
with an rpi3 most stuff runs well in any of the emulators really.