This link is perhaps a good starting point: https://en.m.wikipedia.org/wiki/List_of_MT-32 … _computer_games
As a general guideline, the music for games released up to around 1992, would have been written on a Roland MT-32. For some of these games (released in 1990/91), patches were released to remap the instruments to also support General MIDI (albeit with some mixed results).
The music for games released from 1993 onwards (up to the point where CD audio became more popular) were all written on a General MIDI synthesizer (the most popular one being the Roland Sound Canvas SC-55). Some of these did for a while still support the MT-32, but these were just remapped from the General MIDI instruments.

So, depending on when the game was released, will determine the best suitable synthesizer (instrument mapping) to use.

Another factor is of course the quality of the samples being used on the relevant synthesizer. Once General MIDI became the standard, many players entered the market with so called General MIDI compatible sound cards or add-on Wavetable daughterboards. Some were just plain horrible (hardly better than OPL3 synthesis), while some produced very good examples.

There are quite a few that support both!

Yup. Several Sierra games do. Dagger of Amon Ra for instance. Also, the official patch for Conquest of the Longbow makes that game sound remarkably good with General MIDI.

IIRC Transport Tycoon supported both. That game had fantastic music.