The dwarf varieties are suited to containers, though the bound roots will keep any variety small. Consider small varieties of smooth hydrangea, like Invicnibell Wee White; bigleaf dwarfs like Rhaphsody Blue, Wee Bit "Giddy" or "Grumpy"; dwarf paniculata like BoBo, little quickfire, little lime; or training varieties like Fairytrail Bride; or mountain hydrangea "Little Tough Stuff."
I have a few in pots, and the key is to keep them very well watered.