Best theme for Sonic.

Technically any game's main song is also considered a song for Sonic, such as "Live and Learn," "Endless Possibilities," "Knight of the Wind," or "7 Rings in Hand." However I'm only focusing on themes that are specifically and repeatedly Sonic's (so excluding most of those "game" themes as well as "team" songs like "We Can" or "Sonic Speed Riders" and shared themes like "What I'm Made Of" or "Open Your Heart"). That leaves 3 songs, "It Doesn't Matter," "His World," and "Reach for the Stars."  

    

Background

It Doesn't Matter

The song debuted in Sonic Adventure, returning in the sequel and reappearing in Sonic and the Black Knight. While it did not receive the same attention as the Crush 40 songs, the song is still a fan favorite. There remains three vocal versions (SA, SA2, and the later made S.A.M.E.) and a few instrumentals. 

His World

Even though Sonic 06 received backlash, its soundtrack was immune. "His World" instantly became a Sonic-must. Being the game's main theme it received numerous instrumental versions prevalent through out the game. Some of these were also reused elsewhere, such as in Brawl. Three main vocal versions were created: the game version, Zebrahead's version, and Crush 40's version. 

Reach for the Stars

"Reach of the Stars" was made Sonic's theme after the good reception to Sonic Colors. The song received many instrumental themes through out the 2010s, appearing in almost every many games released in the Current Era. There is now a second version of the vocal song made for Sonic Colors Ultimate.  

Winner

It Doesn't Matter

Actually, I believe "His World" is the best song out of the three. But as a theme for Sonic that reflects his personality and spirit, "It Doesn't Matter" is the best choice. While not worded the best, the lyrics do narrate his point of view. Additionally the genre seems to be a 90s-early 2000s punk-rock mix, which is the best reflection of the character.

The SA2 version was defiantly handled better, but the S.A.M.E. version combines the strengths of each. The Black Knight instrumentals also tamed the song into something quite beautiful (the fan-art music). 

 

Runner-up

His World

"His World" makes a great introduction into the attitude and drama that 06 tried so hard to emulate. The grand instrumentation aside sassy rap and defining lyrics makes it a memorable song. 

I think the Zebrahead and Crush 40 versions are superior and less random the original, however. While it makes a grand theme overall, it just doesn't work as well as a character theme. It's also hard to separate it from 06 or others in the game.  

LOSER

Reach for the Stars

I can't stand the song. It's a 2010s nightmare. Even trying to set aside my personal disgust, I can't see how it makes a good theme for Sonic specifically. How does "the colors feel so right" reflect him? The song was clearly written with the game rather than character in mind. The genre and vocals seem much more suitable for Silver, and the instrumentation is simply too modern-synthetic to reflect a 90s videogame-icon. 

"Endless Possibilities" would have been a better idea since the song is less game-focused (and not to mention it is better by a long shot). "Reach for the Stars" should have been exclusive to Sonic Colors.