Can't fault the Bosch multi cons for 6 and 7mm holes, I'm yet to find a tile they won't go through. Depending on tile density I'll get 3 to 8 holes out of a drill bit in porcelain and ceramics you won't have an issue.
If your wanting 14mm and upward then the erbaurer diamond bits from screwfix are brilliant. Bit pricey but they do last. Just keep them cool by wetting them, same with the Bosch bits.