hi mollie
just a couple of comments relating to your questions:
'snow queen' is an oakleaf hydrangea.
'endless summer' is either pink or blue but not white-flowered.
i have no experience with 'annabelle' but know it is hydrangea arborescens which blooms on new wood. of the ones you mention, it would likely be the best candidate for a hedge.
all of these hydrangeas are deciduous and will not hold green foliage over winter so you will have bare sticks during the dormant season.
in my opinion, none are as showy as our native oakleafs when you consider the fall foliage colors (often brilliant shades of red), layered growth habit, flaking bark and persistent flowerheads. there are some cultivars of it that should remain smaller if space is an issue.
you can check out the site below for images of various species of hydrangea as well as size and site requirements.
spacing of the shrubs will depend on the culitvar and its projected size.
hope this helps.

Here is a link that might be useful: site link

Amen to what Jeff said. My fancy hydrangeas freeze to the ground every year and never bloom. The Oak Leafs are always gorgeous - in drought or rain - and with their exfoliating bark are a four season shrub. Linda

I agree: the nice thing about Oakleaf hydrangea is that it has 3 good seasons of interest: the leaves are nice, the white blooms are nice and they fade to pink and continue to look nice, the fall color is good. Yes the bark is great, making the 4th season nice too, but only a few people appreciate that.

I would not get 'Snow Queen' - the flower heads are too heavy and can weigh the bush down. In my opinion, the species plant would be the best for a hedge.

And yes, all hydrangeas will lose their leaves in Birmingham. But I think the oakleaf hydrangea holds it's leaves the longest.

Well, as you can see I don't know much about hydrangeas. When I open the magazines and see these beautiful full white hydrangeas low hedges on either side of the front porches, I like that look. I am not sure I want just sticks in front of my house in winter. My Oakleafs are lots of leaves with some white pointed blooms and thought they could only work in shade as this gets some sun. I just saw a beautiful cottage on TV yesterday in the Hamptons in NY with unbelievable white hydrangeas in front of the house. This sounds like not an option for me. I guess I should research this some more. Sure like that look.

What is most important to you? Do you want something evergreen?

Perhaps just describe "what" you want and then ask for suggestions of plants that would provide that. Do rank your "wants" in order of importance in case there is a plant that doesn't satisfy them all.

The Sister Theresa mophead has big white blooms that stay white a long time but even here in Dothan, she is just sticks in the winter. Madam E also is a good white bloomer for me, also a mophead.

the planting area sounds like a good spot for any of those hydrangeas with part sun/shade. you could have your hydrangeas in the back of the bed and front them with shorter evergreen shrubs so it would not be bare in winter.
a row of white-flowered azaleas would look nice ('gumpo' is evergreen and very short). also, maybe just the simplicity of boxwoods, dwarf yaupon holly or other low-growing evergreens that you can keep pruned would work, allowing your hydrangea flowers to "peek" over the tops of them.
or, you could do the reverse and plant 'annabelle' in front of other evergreens, cutting them to the ground in winter for a clean look while maintaining a foundation planting of green.
from reading on the web, many gardeners say the huge flowerheads of 'annabelle' tend to flop after rainstorms but they also report that, if they don't prune them to the ground each winter, the blooms are smaller next season.

Hmmm, I am an Alabama gal born/bred/raised, but in last two years been shuttling between Mobile and Massachusetts. I won't explain further, but I must say I've discovered a whole new philosophy of gardening that involves snow, ice and freezing temps.

I recently bought and planted a HYDRANGEA PANICULATA which is going to be a fairly tall rangy WHITE BLOOMING plant. The heads are both fertile and infertile, so it gives a nice lacy effect. It will for sure lose its leaves in the weather of this zone 6 climate. Hard to believe that I come 1500 miles north and go from a zone 8b to only 6, but that is what the local nursery tells me. Feels REAL cold to me!

At this time, the plant has multiple heads/clusters of white blossoms on it.

I bought another plant which is a white hydrangea also, but was shocked to read, when it arrived here, that it would wind up growing FIFTY TO EIGHTY FEET TALL. I immediately changed my plan for this guy, and now my new hubby is building a nice arbor to get it started on its way to the stars.

The hydrangea paniculata looks great, but now I wonder, since no one mentioned it, if it would not like to grow in my Mobile garden?

I know this is very late posting but you have to try the Limelight variety. It is my best blooming variety. I have it in a spot that gets about 4 or 5 hours of sun and it blooms great every year. You will love it. Judy

I know this discussion is about hydrangeas, and I do love my hydrangeas, but how about viburnums? You can get nearly the same look for your property. They're fairly easy to maintain.

The Eastern Snowball Viburnum (Viburnum opulus 'Sterile') is a lovely plant.

Here is a link that might be useful: EASTERN SNOWBALL Viburnum opulus 'Sterile'