Depends what speed you're camera body and how quickly it processes! No point sticking a class 10 in if body only processes and transfers at 25mbs
For my 6d I use these cards memory cow was the cheapest at £23 for a 32gb card
http://www.cameramemoryspeed.com/re...xtreme-pro-95mbs-uhs-i-64gb-sdxc-memory-card/
as compared to My Memory (Out of Stock) and Amazon (almost a tenner more) 
What camera do you have? I used this website to check memory cards were the right ones for my d800. I was able to match the cf and sd cards speeds to stop me buying faster cards than I needed.
http://www.cameramemoryspeed.com

I had the 64gb version of that card and it failed, reports on the internet suggest this is common (don't know if that applies to the 32gb version).Thank you all for your recommendations and advice. What do you think of this Lexar - It's nearly half price of Sandisk. Has anyone used this particular card and had good experience? Cheers
I had the 64gb version of that card and it failed, reports on the internet suggest this is common (don't know if that applies to the 32gb version).
After that fail I bought some transcend 64gb 90mbs cards which have a write speed of around 60mbs which is faster than my camera can write. They are cheap, fast, feel solid (Lexar one did not) and have a lifetime warranty. I now own three of them and will buy more should I need more SD cards.