for me the most important directories to get indexed are -Google Dir -Yahoo Dir -Dmoz -BOTW and last is to find niche and premium directories i often used Directory Critic to find niche dir
You could start submitting to those directories which have high PR and also given more importance from Google's View.
Demoz is the must of consider but their submission acceptance ratio is very low. the next 4 would be any high pr directory that is regularly updated.
It's better to select 5 niche popular directories corresponded to your website. It'll be most useful directories. If you want to select among general directories - see TOP list on greatdirectories.org
Why are you only submitting to 5? If the time you have available to market your site is limited to publicizing it on five sites you might not have very much luck. Every SEO-friendly directory (if accepted, and indexed of course) provides you with backlinks. Building these are important - and they will do a much better job of ranking you in search engines than PR will. I would suggest you get a list of directories, such as Dan's at http://info.vilesilencer.com and submit to as many as you can. If you use this list you will be relatively safe, but otherwise watch out for junk directories. Submitting to directories that have weak editing won't benefit you - and it'll simply waste your time. There's a lot of them out there, so a lot of time to be wasted for anyone not clued in. Also make sure you have a well written title and description prepared. There's not point submitting to 200 directories if you're going to be rejected outright because you thought it a good idea to keyword-stuff your submission.
Start with DMOZ. Make sure you have good contents before submitting site. Here's some high PR directories I use. They have both Free and Premium services. F3 Free Link Directory A1 Web Directory org webworldindex com