I understand the Lion thing, but I feel its a bit weak for his theme as it only plays once (when Griever is around none the less) and I feel the theme really doesn't fit Squall's character beyond its title. I would say its over the top machoness from the vocals and percussions is more fitting of Zell or Seifer but they are not even choices in this case. Hell, Squall doesn't even need to be in your party for the scene where Maybe I'm a Lion plays.

The Oath just seems to always play when Squall is actually having a character building moment as he grows into a leader or fesses up to his true feelings. The somber and heroic feel of the piece is also much more fitting for Squall's personality. These are the reasons I'm choosing it over the other track cause its associations with Squall doesn't work beyond the title of the track.