Sora is 15, he forgot everything from KH1 and CoM, drive forms are cheap and he would need donald and goofy to use at least half of them. He had the power in CoM, but he forgot it all.
Reasons for Aqua are spoilers.
She and Mickey stopped Venitas, and helped in destroying the X-Blade. Aqua stopped Terranort in RG, and Sora has only defeated Terranort's Heartless and Nobody, and those 2 are half as strong as their Somebody. And without having his Heartless and Nobody being able to use a Keyblade, they can be seen as weaker still.
Aqua is the strongest.
EDIT::: Also because of what Raz just said
Yeah you pretty much summed it up, but here is a comparison Sora's Drive Forms, and Aqua's style changes (Someone said the Drive Forms gave him the advantage):
Sora's Drive Forms:
Valor Form: Valor Form allows Sora to wield two Keyblades of the player's choosing at the same time. It specializes in physical combat, but can't cast spells, contrasting to Wisdom Form. Its special ability is the High Jump, which can also be obtained for normal Sora at higher levels. Sora wears red clothes with a red fleur-de-lis symbol. It uses Goofy's power and is based on him. Sora's running speed is noticeably enhanced in this form. As mentioned, this form gains experience with each successful hit on an enemy, making it the easiest form to level up. Sora gains this form when he obtains his new clothes from the fairies at Yen Sid's Tower.
Wisdom Form: Wisdom Form lets Sora float across the ground like on a skateboard, and uses a single Keyblade to shoot enemies with magical bullets, but not physically strike. It is a Magic-based form, in contrast to Valor Form's physical combat. Its special ability is Quick Run, which is a fast dashing technique to move quickly through areas or dodge attacks. Sora wears blue clothes with flame symbols on it. It uses Donald Duck's power and is based on him. This form gains experience whenever a Heartless is destroyed. It is obtained after Timeless River is beaten.
Master Form: Master Form is combination of both Valor and Wisdom forms. It uses two Keyblades, one controlled through telekinesis and the other with the hand. It specializes in both Magical and Physical Combat. Its special ability is Aerial Dodge, a midair jump that blocks attacks (and reflects projectiles). Sora wears yellow clothes with a cross motif. It is based on King Mickey and uses both partners. This form gains experience via collecting Drive Orbs. Every small orb is worth 1 EXP while every big orb is worth 3 EXP. It is obtained in Hollow Bastion by speaking to King Mickey before the Battle of the 1000 Heartless and during the events of Space Paranoids.
Limit Form: Limit Form is a form based on Sora's old clothes, it is exclusive to
Kingdom Hearts II Final Mix, though. It uses abilities from
Kingdom Hearts and
Kingdom Hearts Final Mix that didn't appear in
Kingdom Hearts II. Its special ability is Dodge Roll, a small leap forward that defends Sora from all attacks (and reflects projectiles). The color scheme of Sora's clothes in this form change to that of his original clothes from
Kingdom Hearts to reflect this. When triggered, both partners stay by Sora's side and do not disappear, making it especially useful during tough battles. This form gains experience whenever a Limit Finisher Reaction Command is used. It is obtained when Sora obtains Oathkeeper in Twilight Town. This is the only form that Sora can trigger alone.
Final Form: In Final Form Sora again wields two Keyblades, this time both through telekinesis. It is equally strong in both strength and magic, and is considered the strongest amongst all the other Drive Forms. Its special ability is Glide, which allows the user to fly briefly. Sora wears silver clothes with the symbol of a crown. It is based on Roxas' fighting style (
Final Mix) and uses both characters. This form gains experience whenever a Nobody is destroyed, possibly making it the hardest form to level up. It is obtained randomly after Sora fights Roxas in The World That Never Was; while the first occurrence of the form is random, it can be accessed at any time afterwards. However, there is a glitch where it can be obtained before the fight with Demyx by continously going into any drive form and quiting in Hades' challenge until he randomly turns into this Final Form.
Anti Form: Anti Form is the only form when Sora is without his Keyblade. It specializes in fast attacks and many combos, but lacks the ability to cast spells, shield, recover HP, or use Reaction Commands, which is sometimes required to end boss battles. It appears when one tries to Drive, the possibility of it appearing depending on the Anti Points (a hidden counter, which increases with each Drive by one point EXCEPT by Anti and Final Forms). However, using the Final Form will reset this occurrence and lower the chance of it happening. It has no special ability, is the only form that can not be triggered through the Command Menu, and Sora loses the ability to perform Reaction Commands, which can be especially troubling when certain enemies can only be defeated through them. In this form, Sora becomes completely black with yellow eyes, as well as a dark mist rising from his body, and moves like a Shadow Heartless, resembling the Anti-Sora boss from the original
Kingdom Hearts. It uses both partners and wastes all of the Drive Gauge. This is the only form that cannot level up, and the only one that Sora cannot change back from at will; once this form is activated, Sora is stuck in it until the Drive Gauge runs out, until he exits the battlefield, or until the battle is over. It should also be noted that if Sora dies in this form, he dies as his normal self. The Anti Form can be considered a double-edged sword; while Sora is very fast, his attacks are significantly weaker, he takes more damage than usual when struck, and his movement and fighting style become more feral and less human, running around on all fours and attacking with his hands as though they were claws. Many fans have speculated that this form exists due to Sora's brief transformation into a Heartless, and Tetsuya Nomura has confirmed this: essentially, the Anti Form is the closest that Sora ever comes to becoming a Heartless once again. It is also worth noting that in Halloween Town, the pumpkin on Sora's face turns into the face of a Shadow Heartless, with two yellow dots on it.
Aqua's
Style Changes:
Level 1 Command Styles
- Spell Weaver (known in Japan as Magic Wish): Her own exclusive Command Style; it utilizes the power of light to hover her Keyblade in midair, swiftly attacking enemies while enhancing her magic capabilities as well. Activated by filling the Command Gauge with a variety of multiple magic-based commands.
- Thunder Bolt: A swift Command Style that unleashes powerful lightning upon attacks. Activated by filling the Command Gauge with Thunder-based commands.
- Fire Blazer: A ranged and versatile Command Style that focuses the Keyblade to erupt in flames while attacking. Activated by filling the Command Gauge with Fire-based commands.
- Diamond Dust: An ice-based Command Style that seems to specialize in crowd-control and dealing with multiple enemies. Activated by filling the Command Gauge with Ice-based commands.
- Ice Blast: Another ice-based Command Style that uses an ice cream theme. Randomly activated by filling the Command Gauge with an Ice Cream item.
Level 2 Command Styles
- Ghost Drive: Aqua's high speed Command Style and exclusive to only her; it allows her to attack enemies at high speeds while using after-image illusions and tricky movements to her advantage. Activated by filling the Style Gauge with Thunder and Magnet-based commands.
- Blade Charge: In this Command Style, the Keyblade resembles a Light-blue sword. A long-ranged style, as its name implies, it allows the user to "charge up" the attacks for additional damage. Activated by filling the Style Gauge with Fire and Ice-based commands.
- Air Rider: A Command Style that gives Aqua a great midair advantage, it allows her to ride her keyblade around to attack foes from above at high speed. Activated by filling the Style Gauge with evasive, or Zero Gravity-based commands.
Now a real challenge would be Ven Vs. Roxas...