There's no right answer: it depends on the look you want and the space you're tiling.
- Large tiles (600 × 600mm and above) mean fewer grout lines and a cleaner look, and can make a room feel bigger. They need a very flat floor or wall and an experienced tiler.
- Small tiles add extra detail and character, and let you create patterns such as herringbone, chevron or mosaic designs. They're also easier to fit around corners, pipes and awkward shapes, and on shower floors they give more grip and help water drain.