This is an old topic that has never been properly answered in all the thousands of threads about it on the internet. I began reading these threads a few years ago, and after trying webmin/virtualmin, ispconfig, and kloxo, I found kloxo to be the most solid and well-developed. Since I am not running a hosting company in which large numbers of users would access the control panel, all the fuss about kloxo's security was not a concern to me.
Another reason kloxo was appealing is because it was the most similar to cpanel, which I had used for a few years before switching to VPS.
However, as I am now switching to DO, I am interested to see if there are any newer and better control panels out there. While kloxo is excellent, and easy, and solid, it seems it is not under very active development. I would like something more up-to-date if possible.
DO has made it so easy and cheap to create droplets that I can create one for each control panel I would like to test. This will only cost a few cents, since I will only be using them for the time it takes to test, then destroying.
My personal criteria are as follows:
1. I just need to be able to easily administer several domains with common features like redirects, mail, mysql, phpmyadmin, SSL, etc. The basics, as you would see in cpanel.
2. I need it to be lightweight, for the obvious reason that I don't want to pay for a bigger droplet.
So far, here are my results:
RAM usage after fresh install (MB):
Virtualmin: 135 (later dropped down to 102)
Zpanel: 81 (later went up to 99)
Kloxo is decent, but looks slightly dated
Virtualmin is totally out, not even a consideration.
Zpanel definitely wins on design, but their website does not give installation instructions, need to find it in the forums. Searching modules is also done through the forums, instead of via a separate module system like drupal has. Not as full-featured as kloxo, for example, only allows for very simple cron schedules.
Webuzo is a strong contender. It is the most like cpanel, and by far the easiest to install and get working. However, I have not been able to figure out how to get rid of the long list of common app installers it offers. This is annoying.
I'm going to test a few more, but now leaning toward trying zpanel. If it can be optimized to make it as lightweight as kloxo, it will probably be sufficient for my needs.
It would be great if others could test some control panels and leave their impressions. It would be great if there were an industry standard, similar to drupal in the cms world, that everyone could agree on using and improving.