Filter machines — Most coffee makers are drip machines that use filters. This process involves hot water being poured over ground coffee inside of a filter. The clarified coffee then drips into a carafe waiting below. These machines are usually electric and do most of the work for you.
French Press — This is a more manual method of making coffee. The coffee grounds are placed in the carafe and boiling water is poured on top. This mixture is then stirred to ensure all of the grounds are saturated. The coffee is left to steep for a short period of time — depending upon preference. A plunger is pushed down to force the grounds to the bottom and coffee to the top. This device can also be used to brew tea with loose leaves.
Steam method — Machines utilizing this method are the easiest to use and typically the least expensive, but can also be the least effective. The inside of the machine is pressurized with the steam needed to force the water through the coffee grounds. Sometimes the pressure isn't even enough to produce true espresso. The steam in these machines can also get too hot, causing a bitter brew.
Pump method — This machine will pump water automatically into a tank to build up enough pressure (should be at least nine bars or atmospheres) to force the water through the grounds. Water pressure and temperature are kept at the optimal levels to ensure a good cup of espresso. Some of these machines will even have pressure and temperature gauges so that you can make sure they are at the right levels. This type of machine is probably your best bet for higher quality at a mid-level price. Prices are higher than steam machines and the labor is more hands-on, but the quality of the cup of espresso is better.
Piston-style method — This is the real deal. If you are an espresso purist and able to spend some cash on an espresso maker, this is the style you'll want to get. The most traditional way to make espresso, manual force is used to store up the pressure needed to force water through the coffee grounds. This pressure is made by manually pulling a lever that is connected to a spring-loaded piston (hence the machine's name). It can be difficult to master this technique because speed of lever pulling and density of grounds are big factors, but it may in the end produce a darn good cup of espresso and the satisfaction of knowing you did it all by yourself. These are most likely the most expensive type of espresso machine as well.