If we talk about 3rd party MediaWikis, I would say that the best option is not to show any "Help with logging in" by default. Your average website requires a "Forgot password?" link, but that's it. 

If Wikipedia requires a specific help link, ok, but I think it is more the exception than the norm in MediaWiki sites. 

Even massive services diverge:

Facebook doesn't have any Help links near the login (there is a generic "Help" link in the footer, just like we have it in the left column). Not bad for a site where you can't do anything without logging in. Twitter does the same. 

Wordpress.com and GMail do have a Help link inside the login box, basically supporting the "lost password" use case in no more than five lines. I think we are the only ones inviting confused users (not able to even log in) to read paragraphs of text.

After a quick search through a bunch of MediaWikis, I found that Wikia, WikiHow and Gamepedia have custom login interfaces without any specific Help link. translatewiki.net keeps it, but it redirects to their generic help index, a quick fix seen in several MediaWikis. Another quick fix is to point to the corresponding help in en.wiki (a very very dense page,  http://en.wikipedia.org/wiki/Help:Logging_in ) . Finally, many 3rd party sites still have the red link shining.

Even in Wikimedia projects, as soon as you leave the top 10 sites it is easy to find either red links or blue links redirecting to the older "Why register" pages, where users would need to find the specific information about logging in. Only a few find the effort to translate specific login instructions to their own language.