Some people have their preferences but for the most part most people agree their really isnt much difference. There are two things I look at when discussing - or +.
Which does my dvd burner like best? My Liteon drive likes both, but my Pioneer definitely gives good better burns on +r media.
On +r media, you can booktype to dvd-rom (can make more compatible with a wider variety of dvd players.
Myself, I prefer Verbatim DVD+R, MCC 004.