The first three are slow-growing and the last three will get much too big for the space you have described. Plus the Crimson Sentry mildews badly in summer, and Norway maples often get full of aphids when in leaf, drip their sticky poo. And how long do you want to wait for shade, anyway? Even fast-growing trees take years to size up. Another problem is that slow-growing trees often get a lot wider than 12' as well - all those you listed will exceed that width eventually. It won't be like installing a patio umbrella, where you set it up and are good to go, with it being as big as needed as soon as you open it, and never getting bigger than is needed. So something like an umbrella, arbor or trellis may in fact be your best option.

You might consider a large shrub that you can train/prune to do what you want. I have two cotinus - a purple one and a chartreuse Golden Spirit that have both grown like mad in just 3 years. The purple one is 15 feet and the golden spirit about 12. They both have gorgeous foliage and can be underplanted.

You might also consider Heptacodium micanoides which is easy to prune and train. Vine maple might be another option - they like a bit more shade but can take sun with extra water.

Thanks for the suggestions. After visiting a nursery today, I think I have decided on the regular Acer palmatum, the unnamed variety. I don't know yet - still mulling it over.

Just a note to consider a green one. As you want it for shade, I'm assuming it will be in full sun. My neighbour's red-leaved one gets crispy leaves every year no matter how much they water it. They also drop a lot of samaras. 'Bloodgood' seems to be one that holds it colour in full sun with no crispiness. : )

If it is becoming "crispy" in the sun, then it is not getting enough water or something similar is wrong. Here in the PNW, most Japanese maples can tolerate nearly full, all day sun, provided the soil is sufficiently moist The exceptions would be those that are highly variegated or with very pale chartreuse or gold foliage. Red leaved varieties tend to stand up to sun very well and and you see mature red leaved forms all over the region in full sun without issue but even soil moisture is the key.

I grow a collection of some 30 JM's in containers here in full sun, including those with red foliage. The only time any have become crispy is when I overlooked a watering.

If your neighbors are watering frequently and the tree is still showing signs of stress, then there is most likely an issue with the soil. I'd suggesting mulching the area well to retain soil moisture and reduce evaporation.

This is the green one.

Doesn't really make any difference if it is green leafed or red leafed :-) As I was attempting to point out to Kaillean, a correctly planted and cared for red leafed Japanese maple is just as sun tolerant as a green leafed form....in many cases even more so.

I am happy to hear this! I plan to add more of them and right now, I have full sun. I would really like to have 'Shaina' and 'Full Moon'.

To keep these fresh looking and pristine (minimal fading and no burning) in a hot situation all summer you have to pour on the water. As in the same amount that would keep your lawn look like it was spring the whole time - the site for the maples needs to be cooled by water evaporating off of frequently watered turf or large beds, breezes coming off an open body of water, or large pools of shade produced by taller trees in the vicinity. In the wild the tree grows in east Asian woodlands where it rains buckets during the growing season.

Yes, could be a water issue. But my neighbour does water a LOT and everything else in the bed is thriving. Plus I water my adjacent bed, too, so it gets a double dose. So I'd say be prepared to baby it -- maybe more watering than you'd like especially in the first couple of summers. Perhaps the adjacent sidewalk and house is also throwing off extra heat.