Alright, I'll post my favorites from every generation, except Gen 6, since I haven't played Gen 6 yet, because there's no 3DS emulator for some reason. Some of these might be posted already but they are just that good:
Gen 1:
https://www.youtube.com/watch?v=e_5TVp1wSTUDamn, I have no clue how I beat this game when I was like 4 years old or something. But I know that this theme is still just amazing, after finally beating bitchmade Lance and his team full of dragonfags you thought you were done, suddenly you see your rival and he'll say something like he is the best trainer in the world and this shit starts, those parts of silence in the beginning give it a apocalyptic feel almost.
Gen 2:
https://www.youtube.com/watch?v=2XjouKSkSeMAn anon with great taste just posted it before me and I share his thoughts, this song makes you almost sad in terms of nostalgia, almost wishing you can go back to a time where you didn't have to worry about anything at all and just can play video games. Almost makes me cry.
Gen 3:
https://www.youtube.com/watch?v=Y71w6N8HK_QYou just beat the gym in Fortree, which was relatively hard, due to Winona having one of the best selected gym leader teams in the series, enjoyed the great atmosphere there and haven't really seen much yet when it comes to adventure. Well shit's going down from here on and it's going down hard. When you get onto this route you'll realize that there will be a lot to come and can't even imagine what.
Gen 4:
https://www.youtube.com/watch?v=PWKA-JGA-3MDo I even need to explain? My favorite song in the whole series, really distortional and weird, fitting for the game situation you're in.
