I looooooove credits themes, and Pokémon is no exception, here's a personal ranking and some thoughts:
10.
SwSh: Another Hall of Fame rendition, but with more sense of finality. Love the electric guitar and orchestal mix.
9.
USUM: Happy, energetic tune, with a Trial theme rendition in the second half. A nice farewell to Gen 7 and the 3DS. But I dislike that it slaps SM The End theme, which doesn't fit at all in a black screen.
8.
DPPt: After those intense final battles, what a better way to end the journey with a calm guitar song? Then it becomes more lively and full of energy, to finalize with a piano as the hero arrives home.
7.
XY: Credits song has two parts: a beautiful and kinda underrated orchestal melody and
Kiseki, one of the few songs in the main games with lyrics (that very unsubtly spell out the game's message xd). Fitting choice for the region of beauty and aesthetic. And then
The End theme, to close it up.
6.
GSC/
HGSS: Oh man, the memories. This one spells out: YOU DID IT, MY BOY, YOU ARE THE NEW CHAMPION!!! The remake ver has a more soothing tone to symbolize the end of your adventure in Johto. Personally I am more of a fan of the original ver. But once you think it's over,
this plays, and it can definitely make nostalgic fans shed tears.
5.
SM: A nice remix of the Alola Region theme to close this adventure, it's both happy and uplifting because of the rise of Alola's first champion yet saddening because of Lillie's departure. It loops until it reaches the professors, her ohana, and the song becomes more heartwarming as it ends. Then Lillie's theme comes into play as it says her final goodbyes.
The End theme plays, with the sound of ocean waves and a soothing remix of your House, where it all began...
4.
RBY/
FRLG/
LGPE: This theme is so iconic, the conclusion of many first adventure in the world of Pokémon. My favorite being the FRLG: celebrating first your recent victory, then more suspenseful with some Team Rocket added in, then it becomes more quiet as it begins escalating back to an uplifting song, as the final notes give a sense of: On to your next adventure!
As a bonus, here's
the anime version of it, sometimes called AVANT. Simply outstanding, while kinda ironic that this ending theme is mostly used at the BEGINNING of most movies. Except I Choose You, because its ending it's just the beginning...
3.
BW: This one stands out from the other ones, being much more upbeat from beginning to end than the other ones, as it celebrates Unova is saved and both heroes of Truth and Ideals. This song, or at least part of it, is the only song here that made it to Smash. My favorite part is the second half, it's just sooo glorious when it plays as the dragon appears on the screen. And then the final notes give a sense of: to be continued. But wait, Pokémon games don't have sequels, right?...
2.
BW2: Now this one gives a bigger sense of finality, as your adventures in Unova (as well as the whole DS era) come to an end. Unova is saved for good this time, you are the new champion, the song begins as the fireworks light up in the sky. After all of this, you deserve a well earned rest. As the player comes back home to meet her mother, the theme reaches its soothing conclusion. And a
music box to close it up. Goodbye, Gen 5.
1.
RSE/
ORAS: THIS THEME. It begins with a calm, soothing piano piece. In the original, we get to see our hero cycling in the sunset with the caught Pokémon being displayed as the song gets more triumphant, reaching its highest point when your starter appears. The remake amps it up and becomes a beautiful Hoenn medley while it revisits your adventure and your partners. Both versions end with a nice callback to the RBY credits. Simply majestic. Oh and who can forget that
lovely piece at the end.