I have an existing Enterprise Wiki Site and I would like to convert it to a Publishing Site. What's the difference between a Publishing Site and an Enterprise Wiki Site. It looks like both types have the publishing feature so is it just the content types in the Pages Library?
The type of pages available by default (wiki vs. article and web part pages) is the primary difference.
Since wiki pages in 2010 allow for web parts to be inserted, many people are now choosing enterprise wiki sites over publishing sites. The only big thing you lose with wiki sites over publishing sites are page layout templates. Wikis have some basic table based layouts, but those aren't as easily customized. If you have a number of custom page layout templates, then a punlishing site would still be better.
To add what John said, Publishing sites are better when you are doing a .COM public facing site, when you need more publishing controls, more control over who can author, edit & publish, and when you want to enforce a specific look & feel & brand.