It depends on the work you plan on doing with it, most are capable of doing accurate work, but it will take more time than with a dedicated lathe or mill.
I usually suggest buying a good solid lathe first, (12 x 24 or 12 x 36)with a little ingenuity, you can do small milling jobs on it, but still turn accurate work easily.
The last time I visited Greenfield village, the machine shop there,
(Armington & Sims machine shop) http://www.hfmgv.org/village/libertycraftworks/armington/default.asp#qtvr
I don't recall seeing any horizontal mills like we know today, there were lathes, drill presses, and shapers, but on horizontal mills.
Don
