Blends or Single Origin
This is a very difficult decision to advise on. However, I would recommend that if you want to drink your coffee with milk, particularly espresso, choose a blend. If a black filter coffee is your preference, then choose a single origin.
With a blended coffee, most of the time, specific single origins have been chosen to use in that blend that create a complex and balanced espresso while still having a milk-based beverage in mind. The coffees have been carefully selected to provide increased body, some delicious brown sugaring flavours, or to simply add some floral complexity in order to help balance the espresso.
A single origin coffee is from a single known geographic location, such as a farm or estate. This allows the coffee drinker to appreciate the specific nuance that a particular growing region provides.
Having said all that, can a single origin work well in milk? Absolutely. Can a blend work as a black? Of course.