just purchased an espresso maker, the Mr. Coffee $30
By standard definition espresso is extracted from heated water under atleast 8-9 atmospheres of pressure. To exert that amount of force a pump of some kind is needed.
I don't know if no one gives a poop, but you're asking about beans/roasts for espresso for a machine that won't really make espresso.
Machines using steam pressure don't go past 1.5 atmospheres, as far as I've read, so you'll get strong coffee out of them but it's not technically espresso.
For espresso, fresh roasted beans give the best result. They bloom well, offering a more even extraction when ground fine and evenly, and the tasty oils and components that make for good crema and flavour haven't been lost to oxidation.
Good balanced blends of beans from different origins are suggested since blending bean characteristics results in more rounded, complex, flavourful shot however many good quality single origin beans/roasts (one single type of beans) have great character and to avoid some of their pleasant notes being lost in blending they make a good espresso on their own.
Espresso does not need to be dark roasted either. Lighter roasts also make good espresso. Espresso is strong because, under pressure, more elements of the bean are extracted than by any other method I'm aware of. It's concentrated essence of coffee. That doesn't mean it has to taste overly strong or bitter. On the contrary, good espresso is rich tasting, smooth and sweet with notes you won't taste in brewed coffee.
In the end the type of bean, blend and roast comes down to personal taste. Choose as fresh roasted, high quality beans. Generally grocery store coffee has sat too long and isn't fresh by the time it finds the shelves. Buying fresh roasted beans from a respected roaster is one way of ensuring freshness.
As well, coffee is sensitive to extraction. The more even, the better. Evenly ground coffee assures even extraction which boosts the quality of the brewed cup regardless of extraction method.[/quote]