Can’t Bribe Ultima Weapon

There are only two released versions of Final Fantasy X: the regular edition and the international edition.

The regular edition was released in the Japanese and North American regions.

The international edition was released in the Japanese and European/PAL regions (released simply as Final Fantasy X there). It contains the things you listed:

• An revised sphere grid with new abilities and an expert mode
• New "dark" Aeon battles

as well as a number other minor changes, as detailed on the Final Fantasy Wikia:

The Dark Aeons and Penance, all powerful superbosses, were added, as well as many minor changes to dialogue, scenes, the Celestial Weapons' key items (Japan only), characters and armor & weapon customizations, such as Ribbon. The release also includes a bonus disc with behind the scenes making-of features of Final Fantasy X, and a special movie prologue to Final Fantasy X-2.

The European release has the the Dark Aeons and Penance, as well as the new equipment abilities, but didn't change the name of the Celestial Sigils and Crests. As with previous PAL conversions of Final Fantasy installments, the game has noticeable black borders and a slower running-speed as a result of poor PAL conversion. The black label version includes a bonus DVD with the title Beyond Final Fantasy, which includes various interviews with the game developers, as well as two of the English voice actors. Additionally, it also includes trailers of various Square games, an art gallery, short biographies on Nobuo Uematsu and RIKKI, as well as a music video of RIKKI performing the song "Suteki Da Ne".

Some versions of Final Fantasy X: International have a glitch, whereby if the player goes to the area where they fight Dark Ifrit it is possible to slip past the men blocking the way to Home, and thus, be able to return to the story at the events in Home with Yuna in the party. This glitch can be repeated after the first time it is used.

There isn't one definitive answer for which is the best Overdrive mode since it's dependent on the character and who you're fighting.

For grinding out regular enemies that you kill pretty quickly, Warrior or Slayer is probably your best choice since you'll be doing most of the damage.

For enemies that hit you with more powerful attacks, Stoic or Comrade might be your best option for your damaging characters whereas Healer could be used for Yuna.

I would avoid using Ally since it charges very slow. I would also avoid Coward, Hero, Daredevil, Tactician, Avenger, Sufferer, Victor, Victim, Solo, Dancer, or Rook since none of these are very well suited to grinding.

You can find a complete list of all the different modes here along with how to make use of each mode.