If i buy a DVD writer that can support both the "-" and the "+" formats, which format disks should i buy? I mean is there any difference in the quality of the recording or in where i can use the disk afterwards?
Depends where you're using the discs. If you're using a standalone, check dvdrhelp.com, where there is a comprehensive list of compatibility with various players. In general though, go for whatever is cheaper in your area.