Try before you buy. Choosing the best chair will take more than a few minutes on a showroom floor. Check the retailer's return policy; you may be able to test the chair for a couple of weeks and send it back if it's not the right pick.
How often will you use the chair? If you're going to spend hours in your office chair without a break, it makes more sense to splurge on a chair with as many ergonomic adjustments as possible. If you're buying for a home office that you may only use an hour or two every day, other factors such as budget and style might influence your decision as much (or more) than adjustability.
What kind of work will you be doing? If you'll be moving around a lot, or you work in a highly collaborative space, you may want a smooth-rolling, scuff-resistant task chair with a smaller footprint. Arms might not be necessary, and you may not need very plush padding if you won't be sitting for long periods. However, if you'll be sitting in front of a computer without many breaks, you'll want a deeper seat with a higher back and lumbar support to ward off aches and pains.
How do you prefer to sit? If you tend to lean forward, certain task chairs that allow a more forward tilt might be a wise pick. On the other hand, if you like to recline while working, you'll want to check your chair's tilt limiter to make sure it allows for your preferred range of motion. If you prefer an unconventional position, such as cross-legged with a keyboard in your lap, you'll want a chair with width- and depth-adjustable armrests that won't get in your way.
Do you have existing aches and pains? If your lower back gets sore, make sure your chair has adjustable lumbar support. If you're prone to aching legs, make sure the seat has a sloped front (sometimes called a "waterfall edge") to allow adequate blood circulation -- and be sure your feet can comfortably rest flat on the floor. However, keep in mind that while a good chair can keep pain to a minimum, no chair can cure chronic pain -- and experts agree that it's best to alternate long periods of sitting with standing or walking around. You may even benefit from a standing or walking desk, both of which we cover in our separate report on standing desks.
Does your workspace have solid floors or carpet? Most casters will roll smoothly on hard surfaces, but that might not be the case with carpet. You may want to consider a chair mat in that case -- it will also save your carpet.
Consider your upholstery choices. Mesh promotes airflow and helps keep you cool -- potentially a good pick if you sit for hours at a time. Leather can offer a plush, luxurious feel, but it can also retain body heat. Vinyl is easier to clean than leather, but has the same breathability problem. Fabric is comfy for most, but is also most prone to stains. Higher-end fabrics will likely be more breathable and stain-repellent, however.
While a large employer might view costly office chairs as a necessary investment, it's harder for individuals to stomach higher price tags. One way to snag a quality chair for less? Buy used. While sites like Craigslist might be worth a look, also check office furniture outlets or liquidators. These resellers buy retailers' excess stock and used chairs from defunct businesses, and they're likely to have a better variety than you'll find using person-to-person classifieds. Just be sure to check out any used chair thoroughly, testing all functions and examining parts and upholstery for excess wear. Sticking to well-known models will also make it easier to order a spare part if the need arises.