Easy hydrangeas come from the family Hydrangea arborescens. If you can keep it alive, it should consistently bloom for you, because it flowers on new wood every year. "Annabelle" is a widely planted cultivar hardy to zone 3, but it should perform well in colder areas with good snow cover. This plant would probably be the easiest to grow.
Medium hydrangeas (Hydrangea paniculata) bloom on new wood, but only if it has grown from an older stem. This means you must keep some of last year's wood alive through the winter. This shouldn't be too difficult with a decent snow cover or some mulch. Most of these plants have white flowers that turn pink as the season progresses. The best (and probably hardiest) of these include "Limelight", with flowers that turn from green to white to pink, "Pinky Winky" with long, bicolor pink and white blooms, and "Quick Fire" with very early blossoming. "PeeGee" is considered quite hardy and could make a good choice, but many of the newer cultivars tend to droop less and are even more attractive.
The most difficult hydrangea to grow is Hydrangea macrophylla, the lovely pink and blue flowers that are everywhere on the West Coast. These flower on last year's wood and are very picky about growing conditions, preferring light acidic soil and high humidity. However, there are several new varieties that will also flower on new wood, which means that if you can keep it alive, it may flower for you. "Endless Summer" and "Penny Mac" are both hardy to zone 4, and "Blushing Bride", with white flowers that mature to pink or blue, is hardy to zone 5. These picky plants are probably best left to very ambitious hydrangea growers in this climate.