My take on how to promote and make accessible your works for citation is as follows:
For your global library:
Pick a format. You won't get it always right. Mathematicians and physics will prefer bibtex, biologist and health-related researchers probably will rather have something that works directly on their word (EndNote). In any case, I feel that getting all the citations of an author from his/hers webpage is not that common. People will just pick those articles that are really relevant for them.
For each individual article:
If you don't want to complicate yourself, just add the DOI. Most journals have citation tools to download in multiple different citation formats. If you want to get creative, this same citation tools will provide the links for quite a lot of formats (I guess some journals will offer more options than others).
This option should be that much easier and allow for a more flexible way for your visitor's to actually pick whatever they are really interested in.