Any rebloomer that YOU like would be a good choice. Now is a good time to go hydrangea shopping since many small and medium size nurseries have received new stock. As long as you plant them in well draining acidic soil where they get some shade in the afternoon, any winter hardy variety will do well.

One caveat - for some reason, the original ES has an unusually high degree of hardiness issues in Zone 5 in this forum. We sometimes suggest that it be winter protected in Z5 as a result. The other hydrangeas in the ES Series or the ones in the F&E Series have not had this type of problem. So if you see one locally that you like, grab it, plant it and enjoy it.

Endless Summer Series:
http://www.endlesssummerblooms.com/en/consumer

Forever & Ever Series Website:
http://www.foreverandeverplants.com/Index.aspx/GardenFavorites/Hydrangeas

As always, maintain the soil moist -not wet- and expect some wilting during the summer months as the plant adjusts to your garden and gets over transplant shock. If the shrub wilts but the soil feels moist, do not water as it will recover on its own by next morning.

To determine when to water, insert a finger into the soil daily to a depth of 4" and add 1 gallon of water when it feels dry or almost dry. Make a note in a wall calendar when you water it. After 1-2 weeks, review the information on the calendar. Set up the sprinkler to water 1 gallon of water on the same frequency that you manually watered (every 2/3/4/5 days). If the temperatores change 10-15 degrees and stay there, use the finger method again. It is best to water early in the mornings; water the soil, not the leaves if you can help it (minmizes the chance of developing fungal infections in the leaves).

Do not bother fertilizing on year one as the potting mix will be full of those round fertilizer pellets. Next year, fertilize it with a 1/2 cup to 1 cup of compost, composted manure or cottonseed meal in June. During the rest of the growing season, feel free to add coffee grounds, liquid seaweed or liquid fish but stop all forms of fertilizers in July to make sure that the shrub goes dormant in time and that new growth does not get zapped by early frost.

I have found Twist n Shout to be a tougher plant, not needing as much water as ES Original.

I don't understand the supposed hardiness issues in Zone 5. Endless Summer does great in my cold Zone 4 with minimal winter protection.

On personal observations of the F&E series (widely available at Lowe's), their stalks and leaves seem way more beefy than the ES macrophyllas. This all means that they are much less likely to have droop and only wilt slightly compared to some regular florist hydrangeas. Common sense definitely brings into question the natural water retaining abilities of ES, especially in the early stages. To me, the leaves and stalks are much thinner to begin with.

I think all hydrangea are water wh*res in their first year, ES in particular. But that pays off in the long run. My largest ES needed a drink just about every afternoon in her first summer. By last year, that was year 3 or 4 for her, we had disgusting high temps all summer and very little rain (why our area wasn't declared a drought zone is beyond me). I think I only saw her wilt twice. My Nikkos, OTOH, nearly died.

Check out Blushing Bride Hydrangea for your mom. I really think this is a pretty plant with some interesting color variations.

Here is a link that might be useful: More on BB

I would recommend checking out the Forever and Ever series. Definitely superior to 'Endless Summer' in terms of the color quality. 'Red Sensation' and 'Blue Heaven' are too of the deepest reds/blues respectively that I have seen. 'Endless Summer' is a great plant and I have several in my yard but she is somewhat underwhelming in the color vibrancy department. 'Twist-N-Shout' puts out strong pinkish-purplish blooms (bluer if you are acidifying) so consider her too. Twist-N-Shout is a lacecap which people either love or hate. I personally prefer them to mopheads in most cases.