WebMin/Usermin (free) is Perl based and does all that WHM/cPanel can, plus a bit. Being Perl also means that it can be easily adapted should you need something different or additional.
If you need additional "Visual Aids" you can bolt VirtualMin on to Webmin.
With WebMin or cPanel you can still make changes using SSH (shell) without 'breaking' the GUI. However for Linux servers you should avoid Plesk, it is a resource hungry PITA, that WILL 'break' if you have the audacity to fix things yourself.
Plesk works okay on Windows servers but here again will break if you have console or remote access and go and 'tweak' things outside of the Plesk UI.
Another problem that may raise it's head with cPanel is, that it uses a slightly different format for it's zone files so you cannot simply scp or rcopy zone files to another BIND server as a backup or for a DNS cluster. To cluster cPanel DNS you have to deploy another cPanel licensed server or cPanel DNSOnly installation. The DNSOnly license is currently free IF you have a full cPanel license.
Best control panel for customer is cPanel and other panels are Direct Admin, Site Worx and VirtualMin(Free).
cPanel is best because of its so easy to use it and automation of many thing like creating DNS record. In other panel its hard to create some services or you need to do lot of things but in cPanel one click is enough.
Though having said that, ... ... If you ONLY use the GUI control panel for server management, you may not have problems, on the other hand, ... If you have shell access and make changes over SSH you will probably 'break' Plesk.
I have tried several different control panels, and have just decided to stay with the one, which is CPanel. CPanel has come a long way, they have the best type of GUI which is very user friendly to the consumer. CPanel offers so many features, and allows for installation of free scripts with just the click of a button. I have also created addons for my customer's cpanels, one of which allows them to submit their site to search engines and increase their search engine rankings. So, you can't go wrong with CPanel, highly recommended.
cPanel is the best but you can check all of these too. WHM, Plesk, DirectAdmin, Core-Admin, InterWorx, ISPmanager, i-MSCP, Froxlor, Vesta, ZPanel, Sentora, Webmin, ISPConfig, Ajenti, BlueOnyx, CentOS Web Panel, Virtualmin.