I chose Sound Blaster Pro in sound settings. Is this the best sound available?

It'll save me sifting through settings.

That depends on what ends you're willing to go to, and just how much physical hardware you have.

SimCity 2000 in DOSBox has 1 option for sound effects, and 5 options for music! DOSBox seems to emulate an IBM PC speaker, a Sound Blaster 16, and an MPU-410 MIDI device. Sound effects always go to the SB16. Music can go to the PC speaker, to the SB16's FM synthesizer, or to MIDI; the game has 3 different MIDI banks.

For sound effects, I use Sound Blaster 16 (GOG's default). Some other options do work, because the SB16 is compatible with some other sound cards, but they all seem to sound the same in DOSBox.

For music, your 5 options are:
1. Roland MT-32/LAPC-1 (GOG's default) plays MIDI with MUSICFILES=MT
2. Wave Blaster plays MIDI with MUSICFILES=WB
3. MPU-401 General MIDI plays MIDI with MUSICFILES=GM
4. Sound Blaster 16 uses FM synth, sounds more artificial
5. PC Speaker beeps, sounds awful

DOSBox always plays MIDI through your computer's MIDI synth. All 3 options (MT, WB, GM) use the same synth; the only difference is in the music from the game. Roland/MT might use more instruments, so it might sound better than WB or GM. If you change the MIDI synth or soundfont in your computer, it would be like a different band playing the same music.

If you pick SB16 or PC Speaker for music, then DOSBox emulates the synthesizer and plays the result on your computer's audio, so you don't need a real SB16 or PC Speaker. I have switched to the Sound Blaster 16 for music. The SB16 sounds less like real instruments, but pairs well with the graphics of SimCity 2000.

I don't know the particulars of SC2000 music, but in most games Roland and GenMIDI music are not 100% compatible. It's better to use Roland music only if you are using the real thing or an emulator like MUNT alongside DOSBox, otherwise go with General MIDI.

GOG are morons for setting it to MT-32 by default when they don't include a working MT-32 emulator (or rather can't because of the ROM needed).

The result is that casual users will be getting MT-32 MIDI sent to their computer's general MIDI and all the instruments will me mis-assigned.
They should probably set it to General MIDI by default given that it will be supported by pretty much any computer.

Late to the party, but I think that SC2000 was composed for General MIDI - so, General MIDI with a virtualMIDI synth and a good soundfont would be best, followed by MT-32 (if you've got the ROMs), then Soundblaster.