There are two basic types of machines. Semi-automatic and Automatic:
Semi-automatic machines have a single button which operates the brewing head. Coffee is put into the brewing handle (or portofiltro) and placed securely in the brewing head (also called group or piston). Then the button over the head is pushed which begins brewing. The coffee levels are regulated by the operator. When the disired level is reached, the button is pressed again to end brewing.
Automatic machines have 4 individual programable buttons. After the coffee is placed in the machine, the button corrisponding to the desired level is pushed. This engages the brewing cycle that will measure the coffee brewed and will shut off at the disired level. (Note: The automatic models also has a manual button for unprogrammed levels)
The other considerations are, the number of groups and boiler size:
Machines come with 1-4 groups (brewing heads) however we do not recommend 4 groups machines. Here are some reasons why.(pro & cons) They also have different size boiler capacities. Larger boilers have more steam capacity and much less down or recoupe time. Today, steaming ability is a primary factor in a espresso machine purchase. The Brugnetti brand of machine boast the largest boilers in the industry, with a 4 group machine capacity of 28 liters!!!
What type of machines would you like to see: