If you're going to chooose between these 2 I would say: Always go for Ritek. Ritek might be hit and miss but princo is miss for sure. There is almost no lower quality dvd-recordable availablethan those of princo. Just search the words "Princo" and "Quality" and you'll know what I mean!
If you want good quality media, you should stick with Taiyo Yuden, Verbatim (MCC) and Ricoh.