I just switched over to Linux from RISC OS on the RPi.
On my desktop systems I have used Puppy Linux for quite some time.
On the RPi I am trying Raspbian first then once I get a good feel for how it behaves I will look at the current Puppy Sap6 and see how that does. If I think that I like the Sap6 Puppy I will start playing with Woof (just as with an x86 Puppy) and see how far I get.
All of this means that I will not be doing much productive for a while as I do not wish to lose progress do to OS switches and experiments though I already have a feeling that Puppy will be the way to go. I am only starting with Raspbian as most everyone seems to think that it is the one to use, I am not sure that I agree.
The Raspberry Pi is an ARM computer, that runs many Operating Systems, including Linux, RISC OS, BSD, Pi64, CP/M as well as many more.
Soon to add AROS to the list of operating systems.