I think currently Lexar and SanDisk are recommended, the ones with 80MB/s and higher (Beware! SD cards generally only have lebels with the fastest possible READ speed, not WRITE speed. Write speed can be as low as 1/3 of the read speed. Some cards mention this only in passing, others have an actual number in the fine print)
Remember that there are many things that slow down the camera, particularly jpeg processing. Even if you shoot raw, this processing still happens, at least to the preview thumbnails. If you shoot raw, I recommend you disable Distortion correction, CA correction, Shadow correction, Vignetting correction, Diffraction correction.
Another thing that can give the illusion of a slowed down camera can be the Preview duration. Turn it off, and the camera will feel much speedier.
Before using the SD card, you should format it in-camera. Make sure you backed up all your photos, as formatting will erase them and make them difficult, maybe impossible, to recover. A card that has been taken care of will work better than one that had all sorts of clutter on it.
Originally posted by elho_cid I get a message that "image saving failed" and the photo is lost.
Does that card work normally in other cameras? I have a Sony card that sometimes gives me errors, but it is only that card. It is probably a card issue, not a camera problem. You can test this if you have multiple cameras. I think there are even computer tools that let you test an SD card..? Maybe you can google it
I avoid cards from some manufacturers. We had plenty of threads about this already, so feel free to search for them. Another thing to consider is to buy the cards from a reputable store, as there have been cases where people bought online and got fakes, with poor performance.