You could try out Sabayon Linux, it is basically a Gentoo with an installer and binary package manager. equo (rigo/apper for a GUI). The good thing is that it's backwards compatible to Gentoo's source based package manager "emerge" and a very easy to use.

What Linux/Unix distro you use is up to you though and I will not start a debate. I understand that it makes sense in the enterprise field to only use the most popular and stable OS, to benefit from the Community and Support.

However OSX and Linux Mint, Fedora and Sabayon are the most User Friendly Linuces that I know from my experience. And I've tried most of the stuff on DistroWatch and some that aren't even listed on DistroWatch.

No matter how you dislike Windows, it's still a very solid platform to develop Desktop or Web Applications. I am biased, because I don't like Microsoft, but that doesn't allow me to judge on the effectivity of their software. It does the job. The same, or better can be said about Mac OSX, Ubuntu, Sabayon, Arch Linux and Gentoo which are the most developer friendly environments you can get your hands on. Never force your top developer or sysadmin to use another Linux/Unix than he prefers! Really don't do that. It's like giving your Top-Employee an ugly haircut, he'll leave and not come back or loose effectivity.

Now in practice you might say, this is different and people have their tastes. Totally right and they have their right to like what they want!!
But I introduced an entire development team consisting of about 20 people to Mac OSX and Ubuntu. They had the choice to choose their favorite development environment, but 50% of them switched to Ubuntu, 30% switched to Mac OSX and 20% stayed with Windows. The latter stayed with Windows, because it was too much hassle for them to port all projects and settings over. Even the most fanatic Windows user tried Ubuntu Linux out and was totally blown away after a week of trial.

This helped us to standardize development standards and deploy Ubuntu images to new employees so that they don't have to manually set things up, but can start working after only a few minutes of waiting.

At the time I arrived at the company, I had to use Windows although I requested using my favorite Linux distro. They simply had "no time", to allow me setting the machine up. The result: The Windows box I got was very instable and their ancient svn architecture (without development branch!! All changes were live and they had 500+ customers) continuously helped to crash the buggy Eclipse installation they gave me (weren't allowed to fix it myself).

That made the impression that I work slow, so the Boss sat next to me and stress-tested my ability to live-code what he braindumps into production within 10min while looking over my shoulder. They still use my work and yes, I could finally convert them partly to Git after some months. However I was moved to management and a slow OSX box. Don't get a wrong impression, I had to now work on many APIs, many Back-Ends and integrate our software. And additionally hang on the phone/headset talking with tech or ceo/sales while doing that. So after dealing with their customers and organizing things, I couldn't but quit the job. It was boring and I didn't learn new things, but were forced to use the slow or buggy machine even though I noticeably made things more effective internally. They basically used me as much as they were able to, making empty promises all way long. And to be honest, they weren't even able to do that correctly, they could've used me to do much more, but wanted me to focus only on core-value problems. Corporate culture in a Startup, I hate it! That's my experience, your mileage may vary.