Buying a watch that runs fast vs slow

Oops, sorry David. Seems like somehow I’ve missed your post. I was referring to pre-service at first as I was curious which one would cause “less problems” post-service but somehow I’ve managed to get all my answers.

If you talk about pre service, this doesn't mean much. Accordind to the degree of malfunction is doe not say much about the results one serviced. Who knows how a watch was treated when you get it second hand? for instance a weak/ used mainspring can change everything + Many other factors appart from the regulation itself. Dried oils, magnetism, distorted wheel, bent pivot, etc etc.
Typically, secondhand watches have been in a drawer for year and if noone fiddled on it, the first thing to do is put a new mainspring, have a serious cleanning a new lub. These watches often have a very poor amplitude appart from the +/-