Last time I bought a chair (Humanscale Freedom), I went to Design Within Reach, which also had most of the Herman Miller and Steelcase chairs, as well as Knoll and some others. If you’re in the SF Bay area or Portland, Oregon, Fully (which used to be ErgoDepot, but apparently thought that name was too confusing) has showrooms where you can try out several brands of chairs (notably Varier).
Another brand to consider is the Ekornes Stressless chairs. We have a couch and some lounge chairs, and they’re some of the most comfortable furniture I’ve ever sat on. We happened to find some of their office chairs when we were in the UK, and they are just as amazingly comfortable.
A good chair is a good investment; it’s a shame that you can’t rent them for a couple of weeks or months so you can try them out and really figure out if they work for you.
I want to second all of this.
I went through *several* ****ty office outlet chairs before getting my Embody. The Embody is *way* healthier; I can work longer days and *still* feel better than I did before. (Lower back pain, etc.) My one complaint is that it doesn't do the "tilt forward" thing that the Aeron did.
Furthermore, given the warranty you get, and the typical life span I saw with the cheap chairs, the high end chairs are a substantially better deal in terms of NPV.
If I had people on my staff who sat for long periods of time, they'd all get the expensive ergo chairs. The finances make doing otherwise crazy. Plus, offering them is a nice work place perk that I could give people. So even if it was only break-even, it would still be a net-win to do it.
There are some promising internet only brands, but I'd be hesitant to try them because which ergo chair works for you is very much a matter of your unique physiology. I can't see any option other than just trying them.
My general thought is that the Embody is the chair that works best for the bulk of the population in most situations. Others are good for specific people in specific situations. (The Embody takes a lot of work to tune for a specific individual, so if you are in an office where people don't "own" a particular chair, it wouldn't work. Its arm rests have limited adjustability, so if you need the more advanced adjustments other chairs offer, then you go with them, etc.)