cPanel VS Plesk is kind of like asking "Windows VS Linux". In fact, because Plesk is pretty much IT for Windows control panels, it literally is.
That being said, here's my 0.02 on the matter, but first a bit about me and why I say what I do:
I've been in the hosting industry here and there since way before most of you were thought of (kidding, of course). I started my first 'hosting' (telnet based game, development stuff) company in the mid 90s, way before there was a 'cPanel' or 'Plesk' . Back in the days of Netscape Navigator,
or **shudders** Mosaic
, back when AOL mattered and those dial up tones were like music to our ears... Yes, I'm old. I've been developing code, websites and fun stuff since Geocities (another shuddering memory)
That being said, on the debate of Plesk vs cPanel:
Both have their upsides , of course. Both have their downsides. Plesk is pretty much the only (up to date) system for Windows, and cPanel is the defacto for Linux (at least here in the states).
Having dealt with Plesk, in early years, and recently (as in "where have you been the past year, Tom"), I have to strongly caution against using Plesk in any sort of 'professional' situation. The development team is second only to OnApp in just sheer incompetence and ignorance. It (literally) took a team of individuals close to a year to get Plesk Windows servers running properly, and even then, they still
suffer almost weekly meltdowns . Plesk kept saying "Hey, we're looking at the issue", then just nothing for quite some time.
cPanel's got it's own issues, like I said, ignoring bugs simply because they can, sloppy code to some degrees, but I've never seen cPanel ignore critical, system failing bugs like I've seen with Plesk.
Of course, again, that's just my 0.02.