The problem I've read of is the hard "lip" on the front of seating area which according to some reviewers tends to cut blood flow from the legs for longer sitting periods.
The Embody should be fine in that regard (from what I've read, but I haven't tried it - neither have I tried the Aeron).
I ultimately decided for the "Steelcase Leap" and from my experience this was the best investment I have ever done in furniture.
Before the Leap I was unable (and unwilling) to go sit at my computer after leaving the office - now if I get backpains while at work I cannot wait to get home and into my chair. This may not be the case for everybody but for me it reliefs my backpain.
If you're going to invest in good chairs, give the Leap a spin.