Foxit Reader if you are on Windows, Preview if you're on a Mac, evince if you're on Linux.
I personally do not use Adobe Reader on any platform. I found the alternatives to be both leaner and not lacking any relevant features.
Lately Foxit has been feeling even slower and more bloated than the current Adobe Reader, at least on my setup. I'm pretty happy with SumatraPDF, although it is not terribly featureful so I have Adobe Reader installed as well.
I went back to Adobe after finding Foxit failed to lay out some PDFs correctly (legibly).
sumatra PDF is also a better option
I also use SumatraPDF and find it excellent.
I tried it yesterday, and I was horribly disappointed. Printing a 13 page document took so long (>30s) that I kept killed the process, thinking it had hung. Acrobat 5.something ripped and spooled the same document in maybe a second.