One boiler for both tasks. You’ll have to wait a minute or two between brewing coffee and steaming milk.
The gold standard. Separate boilers for brewing and steaming for maximum temperature stability and speed. what to look for when buying an espresso machine
A "bean-to-cup" experience. It grinds, tamps, and brews at the touch of a button. Great for convenience, though you lose some flavor nuance. One boiler for both tasks