The best cleaner, as far as I'm concerned, is a stiff brush and regular soap. Dishwashing liquid will do. That's what we're talking about. You should also seal the grout and tiles with a penetrating tile sealer both when the shower is new and periodically through the years. Grout and ceramic wall tiles are not waterproof and will absorb quantities of water as the shower is used.
Water is the element necessary for breeding mold and mildew.
Sealing the grout and tiles will exclude much of this water from the tile installation. Use the latex based products. They won't stink up your house like the mineral based ones will. The people who work at these businesses are much more knowledgeable about tile products than, say, people who work at home centers. Home center employees simply have too many products to know about.