mount towel rack/magazine rack to ceramic tile

Don't they give instructions with these things? They should. Generally it is easier to drill through a line of grout, rather than through the tile, if this will give you the desired height. The size bit will be determined by the anchor you are using. You do want to put adhesive (eg liquid nails) or silicone caulk into the hole before installing anchor. The hardware supplied should allow slight adjustment so that you can level the thing. Measure twice- at least- drill once.

drill into tile (not grout joint) using a spade bit made for tile.

You can get special bits for drilling tile -- they come in a variety of sizes and have a spear-like point. Not too expensive and they work well. Go slowly; oil the bit frequently with a light weight oil; and carefully use a center punch to dimple the tile surface before you start (keeps the bit from wandering and helps prevent the tile from chipping).