There is a nice pdf reader comparison at donationcoder.com. Since most academics rely on pdf quite a lot, choosing the right tool may save a lot of time and frustration.
The idea here is to have a tool that opens up as fast as possible, uses as little memory as possible, and lets you move around the pdf conveniently with the best rendering quality.
Some of the tools are obscure (great finds!). Most of them are tiny compared to the standard Adobe Reader, but do suffer quality- and feature-wise.
Adobe Reader 8 has the nicest quality of text, it is beautifully crisp; but even with the speed increase of version 8, the program is still something of a monster.
Foxit is very well known as the freeware alternative, it is not the smallest application of those tested, but it does use the least memory; however, the quality of its output is by far the worst!
Adobe’s new comer Digital Edition is still in beta, and has some annoyances (no custom install, all files added to library) but it is a fraction of the size of its big brother. Sadly the render quality does suffer; though not as poor as Foxit all the other applications tested produced more legible text.