I use them both all the time on several impementations, flavors and versions. My quick assessment is that Cpanel would be the choice for multiple domain hosting account management, while Plesk rocks for single domain accounts esp. if you have many client accounts (I d use the latter)
Further, I find Plesk leaner and swifter to go in and out for routine account maintenance. On the other hand, CPanel seems (or at least SEEMED) to be a favorite among novices...
I hope this helps!