The domain extension doesn't matter. Look for high quality directories that have well edited categories so the directory page will give you a related link. If you have time you should also look for directories that will give you some traffic. They're hard to find, but they're out there.
It doesn't matter. Usually they are all associated with good directories. Check info dirs though, they are usually used in directory networks etc and don't stick around for long.
Domain extensions only matter for branding but can in some cases tell you a little about the site. As an example of another way you can look at it - it can show you how the directory owner feels about the site. Look at it this way - if the site is on a $1.99 .info domain I really don't expect the site to be there long term. On the other hand if you type in various extensions of the same domain and end up at the same place... Well that in my mind says the owner cares enough about the site to spend a few hundred bucks a year on the same domain with different extensions.
instead of focusing on extention, you should focus on quality, traffic and popularity of directory, dont chase pr, pr doesnt represents quality and traffic, its just a number game.