Depends on speed/size. Unfortunately if you want space like 128gb, your sacrificing 80mbps+ speeds. As those cards go only to 64gb.
I have SanDisk 128gb (*newest model on
amazon)
I have Samsung pro 64gb (just bought, one mainly used)
I also have the SanDisk extreme 64gb
Brand wise, id stick with reputable, and locally or
amazon if can. SanDisk is great. Samsung I just bought ($45 for the pro 64gb, wow couldn't pass up), it seems fine. Speeds are definitely there, not sure about long term. I've always used SanDisk, and they're A+. My extreme 64gb I've had now since SP1 launch week. No problems, was my daily until I decided to try out the Samsung. I bought the 128gb for when I want/need massive storage. But at speeds of around 40mbps, it takes twice the time to transfer. So, I haven't really noticed that I NEED the speed, but I always use my faster cards. My 64gb has about 30gb used. I save all pictures, videos, music, data ect on sd. Only programs or 'needed data' on the SSD.
But since I picked up my ravepower card reader/WiFi router/battery back/ect, I have quick easy access to my SD cards/USB HHD'S, so I usually read/write directly over WiFi and onto external drives now.