His side. I would bet money that everything that has happened in this arc will be revealed as part of Aizens master plans from the very beginning.
Warning: Crazy theory (which will probably turn out true due to horrible writing) detailed below!!!
Aizen will reveal that he's known for centuries about the existence of the Quincy hiding in SS through the use of his Zanpakuto. Just as Aizens shikia ability allows him to hypnotize people and make them witness realistic looking illusions, his Bankai ability allows him to do the opposite. That is to say it allows him to see through anything created by reaitsu that would obstruct his 5 senses. This includes kido, seals, and even barriers like the ones the quincy have been hiding behind.
It is for this reason Aizen became aware of them but knew he lacked the power necessary to oppose them. So for over a century he watched them carefully while not letting on that he was aware of their presence. After his preliminary research with Vizard and the primitive Arrancar was complete, he used the incidents of the "rukia rescue" arc as an excuse to flee to Hueco Mundo where he could continue with the next phases of his plans completely free of their (the quincies) observations.
Later after Aizens imprisonment in SS, the Quincies invaded Hueco Mundo and enslaved the Hollow/arrancar in that place, and even captured Harribel. This was done purely because Juha Bach was nervous about what Aizen had been planning after he escaped from their observation of him in SS. After some interrogations and searching they concluded Aizen hadn't done anything that would effect their plans, and that he wouldn't be a problem.
What they didn't know was the things they had been searching for in Hueco Mundo had already been taken from there by Mayuri
long before they showed up. Aizen set it up where Mayuri was "allowed" to find it so he could use it for SS fight against the Quincy. Now that the Quincy have essentially erased most of SS freeing Aizen from his imprisonment, he'll wait in a dark recess until everybody has thoroughly slaughtered each other. Once (most of) the Zero Squad shows up and get distracted he'll hijack their ride back to the Kings Dimension where Ichigo is just finishing up the last of his recovery.
Aizen will get defeated a 2nd time, confessing his faith in Ichigo's power to beat Juha Bach (and whoever else), and restore the balance of the universe or whatever. Ichigo will then go down to SS and face the Quincies at the peak of the battle, beating him in an piss poor excuse for a finale.