Machine Features and What to Look For
Steam-driven units
If you plan on taking the lowest-cost route, you have very limited options in machine choice. The steam-driven unit is packaged with a glass carafe and occasionally is sold with cups and saucers, an instructional video, and perhaps an attachment that "enhances" the milk frothing experience. Outside of these, practically every steam-driven unit is identical.

Pump-driven units
Your choices for machine blossoms in the category. The first feature you want to investigate is whether the machine uses a boiler to heat the water, or a thermo-block. After that, consideration must take place as to the material selection (is the machine housed within metal or is it a plastic case?), the size of the water reservoir, the style of portafilter (I'll get to what a portafilter is), and the controls. In addition are such things as steam wands, drip trays, and plumbing.

Pump machines use two different methods to heat the water, as mentioned above. The first method is with the use of a metal block- the thermo-block. Simply put, water is pumped out of the reservoir and into the heated block where it is quickly heated. It then travels out of the block and into the showerhead where it is distributed and forced through the grounds. Boiler units pump the water out of the reservoir and into a boiling chamber, where it too is heater then pumped to the showerhead and into the grounds. Read the Pros and Cons section for a discussion between these two heating devices.

Both types of pump machines produce heat and that heat has to go somewhere. Escaping heat travels upward and it makes it very convenient to place a "warming tray" atop the machine. Whether it looks it or not, every machine can be said to have one of these. The real debate is whether or not they work. It takes a long time to get a surface warm enough to heat up small china cups sitting on it, and to keep them warm. Home units are rarely on for this length of time.

Water makes coffee. Simple enough. Where does the water go? Well, internal plumbing is the key. Because pressure is the key to proper espresso extraction, some water tends to leak out of various places due to said pressure. Enter the by-pass valve. Very few machines have this and it is a luxury. Especially when it come to cleaning the machine. The by-pass valve, as on their commercial counterparts, works by allowing the residual pressures to escape via a different path after the pump has been turned off. What this means for you is no more hot, steamy water blowing past the showerhead when you remove the portafilter spraying hot, wet grounds on you.

And that leads me to drip trays. Every machine has one. Be sure to find something adequate for your needs. If you have a tendency to forget to clean up after yourself, or if many people will use the machine, you may think about purchasing a machine with a large, deep drip tray. Easy to remove and easy to clean is the ticket.