Check your firmware. Early M8's support SD cards only which max out at 4GB's. Firmware Update 2.0 added support for SDHC cards which allow up to 32GB cards. Updating the firmware is easy, but you'll need a plain old SD card to do it initially.
As for brands you're pretty safe with whatever. Transcend probably isn't going to get a flood of recommendations but they work. In fact in some tests they can be some of the fastest cards on the market. I personally use Kingston brand cards and they've worked well for me. Other reputable brands are Lexar, Sandisk, Samsung, PNY and Sony.