Which driver is the default one for midis on windows 7?
Windows 7 doesn't let you select the midi driver like in WinXP, but you can use the Bassmidi config to change the driver. The default is the Microsoft GS Wavetable Synth.
Is it possible to return to that driver if I do not like BassMidi or if it does not work? If you can, how?
Yeah, just set it back to that and uninstall Bassmidi.
Is it worth upgrading to BassMidi? I do use midis a lot for Zelda Classic.
Bassmidi is great if you find a good soundfont. I recommend the older version 1.06 because the newer ones lag a bit before starting playback.