They're pretty much all safe. I would go with porcelain tile because it looks better and fancier than ceramic tile. The natural stone tiles are also good but they were too expensive for me.
Keep in mind that the tiles will look a shade or 2 lighter in your tank than outside. I guess the lights make the tiles look lighter. So if you want something dark try to get the darkest tile you can. I put tile in my tank and made a thread about it if you want to see.