I bought a SanDisk 32GB class 4. It was constantly going into read only mode due to errors and also the phone was rebooting because I had swap on it too. I think it couldn't keep up with the high demand of IO.
I then bought an Adata Ultra 32GB Class 10/ UHS-1 and it works great. Super fast and reliable:
http://www.ebay.co.uk/itm/Adata-Ultr...item4ac781e2b0

Nice comparison of many cards here:
http://us.hardware.info/reviews/4544...s-a-difference