DVD-Rs as DVD+Rs dont agree with the wii. ive only read about this but to be sure i use Sony DVD-Rs they-re really good or Verbatim DVD-Rs
use DVD-R and a good brand of media such as Verbatim and burn slowly (try 2x, 4x) or else you will get problems with your games running perfectly.
virbatim are better than most. hard drive's are better http://wiki.gbatemp.net/wiki/USB_Devices_Compatibility_List ,