I have a class 10 Lexar 32 GB myself, got it on Amazon during a sale. I run DK's BCM CM9. Everything is running nice and smooth for me.
After reading many threads I believe that Class 6 might be the sweet spot. Also be careful which brand. Shortlist a few cards and research them. Sandisk are probably one of the best. Personally I'm a fan of Kingston. There's also a good Amazon budget class 10 32GB that is said to work very well.
Sent from my Nexus One using XDA
Samsung Note 2 - Dr Ketan's ROM
Nexus One - CM 7.1 final (still using as a backup phone!)