A lot depends on your pillow/mattress combo.
The best pillow is what fits you, and how you sleep.
And a worn out mattress is bad all around..

It's all about how your head gets angled pillow too high, too soft ?
side sleeper - w/ large shoulders or small shoulders?

a few info sites-
http://www.wikihow.com/Choose-a-Pillow
http://www.pillowadvisor.co.uk/how-t...illow-for-you/
http://www.ultimatesleep.com.au/expe...-right-pillow/