The faster the card, really the better. If you get some random off brand, who knows where that card came from, and if the speed rating is even accurate. Some places house brands are pretty good though, I dunno who makes Microcenter's memory but they are very cheap and have yet to have a problem with them. However the real issue would be reliability. It's always a good idea to backup your card, but I rather have my data and photos on a name I can trust. 60 bucks for the PNY 32gb class 10 was a good deal for me.
On this particular phone, you can consider the SD card like your computer's hard drive. Would you really go get some off-brand from ebay for your PC to save a few dollars? I know I wouldn't. Not worth the headache of losing important data.
Device: Motorola Dynatac 8000X