I got a 64GB Sandisk SDXC card which was giving me some problems at first. FAT32 would give noticeably slower speeds (music skipping, etc.) whereas exFAT was quick but would often give errors when writing to the card.
I went and formatted it, removing the small (~16mb, I think) offset partition, and reformatted as exFAT and it's been working fine since then.
When putting it into my PC from the phone I get a "storage may be corrupted" dialog, but simply clicking "find and fix errors" makes it work fine straight away