Some important points to choose for directories before submitting your sites:

• Unique design directory
• Offers deep linking option, at least three or more.
• If paid directory, choose the one that offers various price range for site review.
• Directory contains brand name or unique logo.
• Pages indexed by Google or other search engines, if you care about Google PR value.
• Site review time is less than one week.
• Customer service or support. The faster response, the better choice.
• Directory hosted in good or reliable hosting company which means less downtime.
• Directory does not content Google Adsense or other advertisement including pop up advertisement.
• Directory owner or company has several sites (other directory or sites) in their networks.
• Directory has more than hundred back links in Google search engine.
• All the pages in directory are search engine friendly.
• And the last and most important thing is if you satisfy with the directory (design, contents, etc. ), you can submit your site without further thinking.