Or, if you can find (or be bothered finding) a butcher who cures their own ham, it's more likely that they'll do it in a more traditional way and less likely that they'll use some of the chemicals (sulphur dioxide being one, from memory) that commercial smallgoods manufacturers use to speed up from memory. Likewise a good deli is more likely to supply better quality hams than the supermarket delis.

Leg ham or ham off-the-bone is a much better choice than pressed meats (including pressed hams - if it's square, avoid it). Not only is it an unknown quantity which cuts of meat go into pressed meats, but they have higher fat content and lots of other things added as well.