It would depend on the purpose of the link directory and if you own the link directory, or if you are a webmaster that wants to post a link on the link directory.
Webmasters seem to prefer link directory websites that do not use "nofollow" attributes on link tags.
Link directories that use directory to use "nofollow" are able gain more of a benefit from the Google PageRank of the websites that are linked within it.
Other factors to consider would include; if directory is part of a website or if the website is a directory.
Webmasters, web developers, internet marketing experts, search engine optimization experts, and online business owners often have different purposes for using a directory. - Some directories are used to promote websites owned by the directory owner.
- Some directories are link directory websites are setup to promote websites that are not owned by the directory owner.
- Some directories are setup to allow webmasters to trade links instantly with the directory itself. (This is commonly know as a reciprocal link directory.)
- Some directories are often added to a website, using a sub-directory or sub-domain.
Directories can serve many different purposes, depending on who you are and what you are trying to achieve.