Base 1 as in a tally? like III = 3?
The reason I've chosen base 10 is that's the way I was taught when I was young - counting on my fingers (I still do it as I'm rubbish at mental arithmetic!). I thought a more logical way of doing it would be to start at zero (first finger - looking at your hands palm down this would be your left-hand little finger) then I wouldn't have to dream up something arbitrary for the zero...