Welcome!
When it comes to high end mixers like the DJM-900 and DJM-2000 then a large part is down to personal preference. You have the benefit of being able to use both regularly so should be able to decide which one works best for you.
Consider cost - what can you afford, though both are similarkly priced.
Both mixers have their own set of unique features, so deciding between these 2 products is probably the toughest Pioneer equipment choice out there at the moment.