My husband loaned me his aeron chair and oh my gosh this makes such a difference for my back. I need to get one asap. Sitting at my desk has basically been agonizing for me for the past year, which contributed significantly to my lack of productivity.
It also has an adjustable lumbar support system..which I think Aeron has too. But I think it's also personal preference so definitely see if you can try both via Craigslist. I got to sit in both at my previous jobs so I was able to find the one that suited me better.