For Sega Dreamcast I like the ReDream emulator free version using the OEM bios, (e.g., epr-21576g.bin renamed to boot.bin).
This restores the default Dreamcast intro (versus the ReDream bios included), corrects glitches with menus in the games, and enables saving the games, etc.
I found the upgrade ($5) upgraded resolutions looked great but the higher resolutions and pixel processes required a lot more computing power. Great simple emulator!