Ahh, I remember asking this question
When I bought my first server here at SM (and my first server ever), I started with Plesk. I really liked the look and feel of Plesk. The OS seemed to have worked well with it as well. Once I switched to Plesk 7 Reloaded, I started having problems. The various components Plesk used was starting to become less stable. Mailman, Tomcat, and Dr. Web acted up when using the "Auto-Updater" and I never did get CGI working on there. suexec never worked (even the psa-suexec which is supposed to be copied over the original suexec).
After putting up with a few last weeks of this trouble, I really had to make the switch to cPanel. I have had cPanel running over a week now and do not regret it. It has been nothing but great to me. No errors, everything works, Fantastico and all that good stuff. I love cPanel now. Before I tried cPanel, I would have told you hands down that "cPanel sucks!", however now, I would strongly urge to stay with cPanel.