Microchipping takes only about a second, it is done while the cat is awake, and it is permanent. Tatooing requires anesthesia, it can fade over time or be covered by fur, and it leaves a tender place while the spot heals. So, my recommendation is microchipping, without a doubt!
Microchipping - I have six tatoued cats and after a few years it isn't possible to read anymore. I had a brittish blue spending several years in my family as our cat just because we never found the owner. He had a tatoue but it wasn't readable. He came to our village by mistace on a trailer when a couple moved in but even though we placed adds in the village they came from we never had a respons. He could of crawled up on the trailer when they stopped for a break. It brakes my heart that tose people never got their cat back or at least got to know that he had a good life and was loved and taken care of.
So - microship!