In the early days I didn't care about the keyboard and used what was there. I tried everything (rubber, silicon pad etc.). Since a couple of years I use almost only mechanical ones though I realized that it makes a difference when using this devies 10+ hours a day. These are the ones I use:
at Work: Cherry G-80 with MX-Clears and Coolermaster Masterkeys L with MX-Browns
at Home: Coolermaster Masterkeys S with MX-Browns
I prefer tactile switches and the Browns are great because they don't drive my room mates crazy. And I don't mind many fancy stuff on the keyboard and the Coolermaster are great "simple".
If I have to use some rubber dome keyboards then the basic series (like Microsoft Wired Desktop 600 in particular) from Microsoft is really good.