So, it's well-known that the Hoenn soundtracks use a lot of trumpets, and it's pretty much the instrument most associated with that generation.
What are the equivalents of this for the other gens?
None because the other regions have good soundtracks
None, really. Just listen to the Route 201 theme or DPPt Battle theme. You have woodwinds, percussion, and horns. It all kinda has that oddly synth-but-kinda-real-sounding soundfont, though. Gen 5 diversified the soundfont and you get things like Driftveil. You can clearly hear a triangle in the background at certain parts while the overall melody is a kind of horn/woodwind synth. Gen 5 used more synth sounds than instrument-likes so certain songs sound a bit more video-gamey than gen 4, while others are very reminiscent of analog music. With again the example of Driftveil as analog, listen to how synth-heavy the Colress theme is. The diversity of the soundfont and its implementation really shows how far they've come from gen 3 where nearly everything sounds like the same instruments playing similar songs. That being said, I still think the gen 1-3 playlists are impressive given how limited the sounds were.
https://www.youtube.com/watch?v=2ajhgkYFCG0
https://www.youtube.com/watch?v=FdFJHhzZ_Bg
https://www.youtube.com/watch?v=zhcA0RkVE-4
https://www.youtube.com/watch?v=L-6JV-M8oxE
