In general, it's not going to have enough of an impact to worry about, particularly since it's an intranet app and not a general-use Internet app. In particular, since it's intranet, SEO isn't a concern, since your intranet shouldn't be accessible to search engines. (and if it is, it isn't an intranet app).
And any framework worth it's salt either already has a default way to do this, or is fairly easy to change how it deals with multi-word URL components, so I wouldn't worry about it too much.
That said, here's how I see the various options:
Hyphen
- The biggest danger for hyphens is that the same character (typically) is also used for subtraction and numerical negation (ie. minus or negative).
- Hyphens feel awkward in URL components. They seem to only make sense at the end of a URL to separate words in the title of an article. Or, for example, the title of a Stack Overflow question that is added to the end of a URL for SEO and user-clarity purposes.
Underscore
- Again, they feel wrong in URL components. They break up the flow (and beauty/simplicity) of a URL, since they essentially add a big, heavy apparent space in the middle of a clean, flowing URL.
- They tend to blend in with underlines. If you expect your users to copy-paste your URLs into MS Word or other similar text-editing programs, or anywhere else that might pick up on a URL and style it with an underline (like links traditionally are), then you might want to avoid underscores as word separators. Particularly when printed, an underlined URL with underscores tends to look like it has spaces in it instead of underscores.
CamelCase
- By far my favorite, since it makes the URLs seem to flow better and doesn't have any of the faults that the previous two options do.
- Can be slightly harder to read for people that have a hard time differentiating upper-case from lower-case, but this shouldn't be much of an issue in a URL, because most "words" should be URL components and separated by a
/ anyways. If you find that you have a URL component that is more than 2 "words" long, you should probably try to find a better name for that concept.
- It does have a possible issue with case sensitivity, but most platforms can be adjusted to be either case-sensitive or case-insensitive. Any it's only really an issue for 2 cases: a.) humans typing the URL in, and b.) Programmers (since we are not human) typing the URL in. Typos are always a problem, regardless of case sensitivity, so this is no different that all one case.