I use a Sandisk SD card myself, as they are supposedly known for reliability.
The speed of the SD card shouldn't make a whole lot of difference, as the reading rate on a standard SD card should be more than adequate. You will still experience excess loading times if running roms directly from the sd card, no matter what type you purchase (as you probably have seen, that's a menu issue that still needs resolution)
I would personally go with a reliable card, and a more common brand name (since lesser known ones may not have yet been tested as being compatible with the menu)
BruceG