Went through a period of only single speed for couple years but now have SS hard tail and a new recently acquired FS (never ridden FS till 2 months ago and i am quite surprised how much i like it!).
I love riding the SS, especially this time of year as things get muddy. Technically mine is a dingospeed (thinks that what you call them) I have two rings at front and back and have to change manually. Reason for this is i commute and ride of road, so its nice to have the two options.
Personally i think if you have got your gear ratio right for you then there's not much difference between SS and geared, if your fit and fast then you will be fast riding geared or SS.
Despite loving SS it is still nice to have a geared bike for longer rides or just something different. As said above if its got 2 wheels then its good, i just like bikes, SS, geared, fixed, rigid, FS or HT.