It's cPanel without a / , not sure where you got that, anyways...
IMHO, cPanel is better than DA and they both have some of the same features, however, cPanel is so fully comprehensive on every aspect of the control panel and anything needed. They will be releasing cPanel 12 sometime in the remotely near future which will give a fresh look to cPanel as well. I just like the interface of cPanel much better and how everything just "works". I have a license for Plesk as well and I have to say I've had more errors with Plesk than anything else and they were stupid little things that take a long time to figure out like down to the permissions on some qmail file that's supposed to be done during the install. I also have used InterWorx and in my opinion, it is right there with plesk and cpanel because it gives so much information and I haven't had a whole lot of issues with it. I personally haven't used DirectAdmin on any of my servers ever, but it looks a little childish and I don't like how the admin panel consists of three sections and you have to search through them to find the option you're looking for.
I've previously used cpanel and have just started using Directadmin. I enjoy the simplicity of Directadmin. From setting holiday messages on email accounts to enabling and configuring spam assasin. It does not hog server resources (the lightest of the lot I believe) and is super fast. I also enjoy the simple skinable user interface.
The only thing I would ask for in Directadmin is unzip/zip facilities for the file manager. If you are using ssh, you can get by without this, but maybe ssh may not be the best solution for a client.
As it stands, I would not go back to PLESK or Cpanel, especially on a vps account with limited RAM.
Can you transfer accounts between DA servers through a tool or even from cPanel to DA? How did you transfer your accounts? I've heard quite a few good things about DA and you're not the first that I've seen switch from cPanel and love it. I might switch to DA until cPanel 12 is released. I've also got a Plesk 8 license I bought a while back, but I don't really like plesk as much.
I can't speak much on the resources used, but I can speak on the simplicity. For someone who has never seen a control panel before, I think that DA is much easer to pick up. I use the enhanced skin and it is very intuitive for users. Yes, I have to deal with 2 or 3 levels, but they only have to deal with the one. I set up most of my users sites, and will even use the cliomail skin for users that just need to tweak email accounts and such.
I've used both, and I don't think I will go back to cPanel.
I used Cpanel, Plesk, Directadmin. Directadmin wins my vote. It is simple but powerful enough to do what I want. and combined with SSH, it is awesome.
Only problem I see with Directadmin is, there is not enough features or templates especially for foreign users. But, probably that has changed.
I used webmin, too. I would prefer webmin over Plesk or Cpanel anyday, too. I can not explain how I disliked Plesk and Cpanel enough. I use 28K dialup modem connection at home, and they were so...cumbersome.