Over the Rim
This model is fitted with a standard faucet. The bowl is filled with water the same way you fill a sink. This is generally the cheapest and simplest type to install. Having a rimless bowl makes easy to clean.

Heated Rim (flushing rim)
This unit has Hot/Cold handles on top, but the water enters the bowl below the rim of the basin.

Spray
The more popular models are equipped with a spray, which provides a gentle shower. There are two type of sprays:

Vertical which has a fountain jet in the center of the bowl, and horizontal, which has special over the rim spout that delivers a horizontal stream of water.

There is a possible risk of water becoming contaminated from back siphonage created by spray fittings. These units must be installed using backflow prevention devices, and should be installed by a plumbing contractor. As usual, consult local building codes before installing.

Combination
Some models combine the heated rim and a vertical spray option in one unit.