No, DVD recordable media isn't all the same - quality can vary widely.
I'd be concerned about buying Ritek DVDR media at the moment, at least until they can get their quality control together. As for the Platinum, never heard of it, sorry!
If you can buy online, Taiyo Yuden make excellent discs...for regular stores, try Verbatim.
May I also suggest having a little look around the Blank Media forum here at CDF
Edit: Haha, Stroppy posted before me...and reminded me about TDK, doh! :doh: