There are several spinning wheel reviews (and groups!) at Ravelry dot com, a free membership place for lovers of fiber who knit, crochet, spin, dye, and/or weave. There are also Ravelry groups dedicated to specific fiber animals, like...rabbits.
Some single-treadle wheels, like my Clemes & Clemes Modern, have a treadle wide enough for both feet to work at the same time, which allows a symmetrical body position. Some single-treadles, like the Saxony-style wheel described above, require an asymmetrical body position, which can hurt after a short period of spinning. Double-treadle wheels also permit a symmetrical body position.
If you'd rather not look through Ravelry, one commercial site with photos of many makers' wheels is The Woolery (woolery dot com).
Of course, for most of humanity's history, all fiber was spun on spindles. The wheel was a relatively late invention, travelling to the West probably from China by way of India and launching a ten-fold increase in Western spinning capacity in approx. the 13th/14th centuries. A general discussion can be found at joyofhandspinning dot com and in the Fall 2011 issue of Spin-Off (also in this blog entry by the editor of Spin-Off:
http://www.spinningdaily.com/blogs/amy/ ... ddite.aspx).
There is no "best" wheel for everyone; there
is probably a "best" wheel for
you. If possible, find a guild of spinners or weavers in your area and ask to be shown how the wheels work before committing to a purchase. (Used wheels are available on Ravelry, too; it's not always necessary to purchase a brand-new $$$ one.)