Each is a good solution with its own quirks. Below are some thoughts, suggestions and things to consider for each...

Potting: Many people pot them and have to bring them indoors during the winter so they will be better protected. You will not need to move them into a garage most likely but will need to move them around as the location becomes more/less sunny. Big pots weigh a lot so get something with casters that can help move the pots. Watering/fertilizing can be a pain for potted plants because you do that often; consider using a drip system.

Ground: Planting on the ground makes it easier to water and fertilize if you have a sprinkler system but maintaining mopheads/lacecaps color is harder. You will need to fertilize more if the soil is sandy; prepare the area by adding a lot of compost. Compost will provide minerals and help absorb/release water.

Pick an area that gets shade starting at 11am during the summer months and where the soil drains well.

Some kinks with the ground idea... If your ground soil is sandy, they will require 50% more water than normal & initially add lots of compost (keep adding a layer more in future years). You often need to fertilize once in Spring when planted in the ground but the soil is sandy, consider extra applications to replace/add minerals used up.

Hydrangeas that do not grow too large will make the best candidates for pots. You can start them in pots 2" bigger than they are now and progressively change them into larger ones every 2-3 years until you get to the max potting size that you want to use. You will need to select a location where they get protection from the sun in the afternoon (say, morning sun thru 11am or 12pm) during the summer months. A windy location can make the pots dry out quickly so look for a location that is not windy. Water frequently if the soil feels almost dry or dry to the touch. And because all this extra watering leeches the fertilizer out the pot's holes, fertilize more often.

Watering suggestions: water only early in the mornings and water the soil, not the leaves. Use the finger method to determine if you need to water. For example, if planted on the ground, insert a finger into the ground to a depth of 4" and water 1 gallon if the soil feels dry (1.5 gallons if the soil is sandy). Check the moisture daily in the mornings for 2-3 weeks and note down in a wall calendar every time that you water. After 2-3 weeks, review how often you had to water and set the sprinkler to water 1 gallons on the same frequency. That is, if you watered every 5 days, run the sprinkler every 5 days or so. If the temperatures change 10-15 degrees up/down and stay there, retest using the finger method daily and adjust as needed. If checking a potted plant, insert the finger to a depth of 2-3". Water the soil from the plant's center crown outwards, towards the drip line. If planted on the ground, add 3-4" of mulch up to the drip line so the mulch will help minimize moisture loss. Add a sliver of mulch to potted plants too. Water less if you notice the plant going dormant in late December/January. The first summer is usually the worst one so keep and eye on the soil moisture.

If you notice that the leaves' edges are turning brown and the brown moves inwards or if you notice that the leaves wilt, the plant may not be getting enough water or the area is too windy. In future years (when the plant is bigger), increase the amount of water. The water estimate given above is for a newly planted hydrangea sold in a 3-5 gallon pot.

Site selection: important that the plants' leaves get shade after 11am-12pm during the summer months. And notice that I keep stressing 'summer months'. The sun now is not too harsh so they can even get full sun in some areas but that does not work during the summer. A plant in the ground can be transplanted if the site is too sunny. If potted, simply move the pot elsewhere.

Does that help you?
Luis