The best of the best hydrangeas according to respected plantsman Michael A. Dirr, in the blue or pink range of color tints (depending on the soil's pH):　

Hydrangea macrophylla ‘Dooley’, pink to rich blue, cold hardy to -11°; mildew susceptible; robust, 6'; shade garden worthy after two years; re-growth with abundant flower buds after some dieback .

H. 'Endless Summer', 'Decatur blue', David Ramsey', 'Oak Hill', 'Penny Mac' - Repeat blooming types; quite similar; flower on new growth; foliage flat medium green; moderate mildew susceptibility; 3 to 5 feet high and wide;  suffered cold damage in trials but the new shoots develop flower buds and fully flowers.

H. 'Generale Vicomtesse de Vibraye' - opening soft cream-yellow, finally pink to blue; entire to serrated sepals; 8 feet high; one of the early French hybrids; stems spotted (speckled) wine-red; medium green leaves; mildew susceptible, shade garden grown; strong growth with no dieback; abundant flowers.

H. 'Nikko Blue'- Popular true reblooming

Hydrangea macrophylla ‘Mini Penny’. Mildew resistant and reblooming; can be grown in USDA zone 4 with winter protection.

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- Courtesy of NYBG Plant Information Service