There's no very simple answer (In before Taiyo Yuden![B]edit: ninja'd by Arachne![/B]) but what you want to do with your disks is somewhere to start. RW disks are for burning to and writing over, and are not good for very long term storage due to their crystaline based physical structure. They also don't tend to be rewritable anywhere remotely near what the manufacturers say!
Lite-on's used to favour +r media, and I've seen posts from lite-on users here that they get better burns with +r. -r should also be fine, and it's more compatable with certain dvd-players. Check out the special Lite-On section of these forums, and do a search for your particular drive to get more relevant info.
More important than dash or plus media is the brand and manufacturer. Generaly cheap media is cheap for a reason. For video, any slight issues with the disk is likely to cause more obvious problems than with data, so definitely buy premium disks. Have a browse round the Blank Media section of the forum and see what is being recommended, in particular for your burner and firmware.
Hope that didn't confuse you more than you started out!