Michael Chang , Jan 14, 2012; 03:06 p.m.
Hi Steven, the class of the SD card designates speed. If you're only shooting stills then write speed won't be particularly important unless you shoot in bursts often.
As for reliability, make sure you buy name brand from a reputable seller to avoid counterfeit cards (very important).
For the cost difference, I'd get at least two Class 10 cards.