Just buy the cheapest card you can find.
The 770 uses the older 7-pin (1-bit serial) interface and a maximum 20 MHz clock, the theoretical maximum transfer rate of the interface is 2.5 MByte/sec. Having a fancy new card that supports 52 MByte/sec won't help.
RS-MMC, MMC-Mobile, Single Voltage, Dual Voltage, doesn't matter, they all work with the 770.