Two-Hand vs Power Stance in DkS2?

Broken Straight Sword on Hollow soldiers (Dex 6, Str 6, Sta 6):

• 1 handed attack (light): 43 damage, 10 attacks in row;
• 1 handed attack (heavy): 43 damage, 7 attacks in row;
• 2 handed attack (light): 52 damage, 8 attacks in row;
• 2 handed attack (heavy): 62 damage, 6 attacks in row;
• power stance (light): 69 damage, 5 attacks in row
• power stance (heavy): 82 damage, 3 attacks in row

Notes: The sword scales ONLY D with strength.

Caestus on Hollow soldiers (Dex 10, Str 15, Sta 6):

• 1 handed attack (light): 90 damage, 8 attacks in row;
• 1 handed attack (heavy): 108 damage, 6 attacks in row;
• 2 handed attack (light): 100 damage, 5 attacks in row;
• 2 handed attack (heavy): 136 damage, 7 attacks in row;
• power stance (light): 128 damage, 8 attacks in row
• power stance (heavy): 144 damage, 2 attacks in row

Notes: The Caestus scales A with strength and B with agility, its power stance light attack is very fast.

Broken Straight Sword + Long Sword (Dex 13, Str 15, Sta 6) on Hollow Soldiers:

• power stance (light, Broken in left): 127 damage
• power stance (light, Long in left): 130 damage
• power stance (heavy, Broken in left): 153 damage
• power stance (heavy, Long in left): 157 damage

Notes: Using the higher damage weapon in the left hand gives better results.

Other things worth mentioning:

• power stance attacks apply on-hit effect twice (once for each weapon);
• power stance attacks are (usually) slower if not chained;
• the left hand hits stronger in power stance.

In the end, power stance is more consuming than two handed, but deals more damage. Also, using a quick weapon in the right and a high damage weapon in the left, can give you the opportunity to strike with your stronger weapon (or both if power stancing) after briefly stunning your opponent with your faster weapon. It's also worth mentioning that you must have +50% of the stats required to dual wield (rounded bottom), while to use a weapon with two hands you need less strength than required (you get +50% bonus to strength).

The only thing I have noticed from power stance is that it has some really cool move sets, such as swinging both weapons at once. And about the stamina drain, it is the same as two handing a weapon if the power stance move hits twice it will drain stamina twice if it hits three it drains three... in sure u get it even tho I probably didn't explain well I am sleepy.

The stamina drain seems significant, but it is actually equal to if you had swung your weapon twice. To think of it very simply you are going to double your damage, for double the stamina, in half the time.

Compared to a greatsword or ultra weapon it can offer similar damage, but also applies status effects quicker, can break poise faster, and generally animates more quickly.