We just did La Nouba. We had seats one row behind the VIP ones and just across the aisle from the golden seats.
The golden seats are a different color (gold/ish). That's the only difference I could see.
While Dan has a point, and I am not an experienced Cirque goer, I loved my seat. There was a solid percentage of the show that was at eye level and I love being able to see the expressions on the performers faces.
On the other hand, I imagine the upper level would provide a lovely, encompassing view of everything going on around the stage.
The theater is relatively small - I was surprised at the size of it. It's an intimate feeling space. I don't think there's a bad seat in the house (except maybe the very front where you would be staring up at everything - just as if you were front row in a movie theater).
So sitting in Cat 2 would save you some money and still give you an awesome show. Cat 1 would give you a different view, not necessarily better or worse depending on your preference. VIP or golden would cost you more money without providing any additional benefit....