From the ones listed... Mechanical Bless/Dear Falling Angel, from King of Fighters 99, still, I believe that nothing beats fighting Adel while listening to "Etude of Revolution".
My overall favorite? A toughie there. For KOF I would have to say KOF 98 Omega Rugal Arranged (eg. the CD versions). "Make some noise!"
For some reason, I really really enjoyed the music of that stage. I was practically singing that one for days after I first heard it. I don't think I've heard catchier Boss music in any other KOF, so far.
My favorites for final bosses in order are: Igniz, Rugal '94, Goenitz, Orochi Rugal '95, Rugal '02, Adel's theme, Slasher Zero, Rugal '98, and the all mighty Krizalid's theme from '99. 10 minutes of pure bosses kicking musical power right there.
I concur with Rhythmic Hallucinations, the theme used for the Orochi New Face Team. The arranged version of the track surprised me at a time when I thought music couldn't surprise me anymore. There's this part I particularly like where the song gave way to a women's choir just chanting, then the heavy drum & bass signature of the song just bashes them down. This is one of those cases where the original, arcade background music didn't impress me so much until I heard the arranged track.
I always thought Geese boss themes in Fatal Fury were really awesome but lets not get there since this is about KOF. Lets see... I liked the Rugal '98 boss theme alot but I also liked the themes with the New Face team in '97 too. Goenitz theme is really cool too. The themes in 2001 was ok but I didn't really like any of the other music from it.
I guess rugal's 98 music.
but his original 94 tunes are great too.
I absolutely love his arrange music that they had in
the best of KOF arranged 94~99
totally awesome, best nazi death dance music I've ever heard.