I have been doing web development for a long time, using openSUSE Linux:  Extremely Stable, Powerfull, All Packages you really need in the Repositories, very friendly support in the forums from some high-power techs.

I also test the sites using the MS-supplied VirtualBox VMs with various IE and Win versions.

I use several Linux versions (most of the ones mentioned here, and several others) for differing purposes.

By far, most satisfaction from openSUSE.  Use it for lots of Multimedia and Photography work, as well.

Gerry
Fraser-Bell Info Tech