Well, we all know Sivir is a master contortionist. Both bandit skins have twisted torsos to an extent and I'd argue that the old one is more so. Also, the old Bandit skin is the only splash for Sivir that had her holding her weapon in the wrong hand.
So as far as Sivir skin unification goes... Bandit is a good change.
The alternate Pax looks cleaned up, but the overall pose is a downgrade. I feel sorry for the people that actually have that rare skin.
Spectacular looks cleaned up with the same pose, so that's good.
Warrior princess is... well... I have no idea. She looks so young. Such a startling difference that I don't quite know where to start to compare new to old. I hated the ugly Warrior Princess splash, but this alternate doesn't really seem like Sivir to me. So... its a 520 skin.
Huntress looks equally bad so I guess the alternate isn't a bad change since it seems more focused on Sivir instead of her weapon.
Overall... I feel that Sivir is getting a good update here excluding the PAX skin.