IMHO none really and tomcat is easier to setup
Tomcat has a larger user community.
Jetty is lighterweight, scales up better, has an extremely responsive developer community who hang out on this forum and email@example.com, firstname.lastname@example.org, and is now packaged as JBoss' default web-container.
This site originally ran on Tomcat. It moved over to Jetty.
Jetty has an AJP13Listener for communication with Apache and all the normal bells and whistles that would expect. If it not there tell us and we will sort it.
Look on jetty.mortbay.org for more information.
Hope that helps,