Try finding the ones that sort on incoming hits and are old and matured. These ones have high PR on subpages and even on sub sub pages. For example adultblogspider.com , this one sorts on incoming hits, so when you send 1 hit a day your blog will be listed on category page which has PR4. If you send a fewer hits your blog is listed on category page 2 which still has PR2. If you can send hits then try getting in the toplist which is on the main page which is PR5. This way you are in control of where your blog is listed, when it isn't on a nice page then you can change it by repositioning the link to the directory.
And that is just one of the reasons, you can likely imagine a few more
I made a topic some time ago that shows how to find good blog directories:
http://www.netpond.com/showthread.php?t=124037