The problem with outdoor tiles is that they get caught in the weather year round. If you live too far north, you’ll want to stay away from marble and porcelain, which don’t fare well in freezing weather. On the other hand, if you live in a sunny climate, marble can bleach and lose its beauty. It’s best for mild year round climates if you’re going to use it outside.
What does work well outside for any type of climate are natural stones. These include granite, slate, and travertine.
Other types of tile could work well outdoors too. I’ve seen glass mosaic used outdoors. Since the glass is non-porous and therefore not subject to damage caused by moisture, which is your main concern regarding outdoor tiles, glass mosaic can add a nice touch to a modern outdoor patio.
Ceramic tiles – and, yes, that includes porcelain, which is a variety of ceramic – are not good tiles for outdoor use. Their water absorption rate is too high. Even though porcelain is durable, it’s best kept for indoor use unless you want to use it in the bathroom – and I wouldn’t recommend that.
Your best bet for an outdoor patio or a pool area is to go with a natural stone tile. If it’s for a pool area, I’d go with something that isn’t slippery, like glass or marble. For a patio area, especially one where you’ll do a fair amount of barbecuing, outdoor cooking, or serving meals, you should stick to something that won’t stain easily. Again, natural stone is the best recommendation.