Kazeshini for PvP and Sogyo no kotowari for PvE.
Kazeshini for pvp because he decreases 10% of attack from enemy assaulters.
Sogyo no kotowari for pve because he gives damage to all partners...
Kazeshini's attribute has speed... so that's a major factor in pvp as well as pve.
Don't see much point in trying to invest in any of these 2 zanpaktous because you can get Ryujin Jakka from UBP and that's worth the price.