The term Whovian was originally coined by the Doctor Who Fan Club of America (DWFCA) in the mid 1980s and has since fallen into common usage to describe a devotee of Doctor Who.
The British term Whonatic predates Whovian by a number of years and originates from a group of Doctor Who Appreciation Society (DWAS) members based in the West Midlands town of Walsall. The popularity of this DWAS subset/local group grew to include members from neighboring towns including mine. My dad was a fully-paid-up and active Whonatic who attended meetings and conventions in Stourbridge, Solihull and Worcester.
So I guess I call myself a Whonatic rather than a Whovian because being a Whonatic is in my genes! It’s not a factional or discriminatory thing. I don’t think for one moment that Whovians are inferior to Whonatics, or that NuWho fans are less devoted that long-time fans. I haven’t got time for that kind of crap! Whovian, Whonatic, Wholigan or simply Doctor Who fan – it’s just a label and isn’t that important.