I only grow Duchess of Albany, but here it is really vigorous, even planted in partial shade. I really like it.

I only have grown Piilu and Voluceau. Piilu is very compact, only about 4'tall so far for me. I have it growing in a large pot with a Northwest exposure. It has grown and bloomed very well. I've never had any disease problems with it. It blooms double and single which is nice.

Voluceau is growing in a dry shady area and is still doing well. The blossoms are very large and look like velvet. I have never had any disease problems with it. I like that one also.

If you can afford them
I would try them all. I have a very small city garden and have 60-70 clematis planted in it. You can tuck them in all over your garden. It is really easy to find places for them if you use a little imagination. You can grow them on shrub, trees, and free standing obolisks. You don't have to grow them on a fence. Here are a couple of photo's.

Piilu growing in a pot

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Voluceau

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Karen

Well I grow Sizaia Ptitsa, Piilu, Duchess of Albany, and Fascination. Royal Velours was just purchased last year from Donahues so it is still in its sleep stage although it has put up a fair amount of foliage this year. Fascination is relatively new for me as well and here are its first blooms and buds this season.
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I really love Duchess of Albany for its vigor. Here it is this year. Not sure if you can tell but it grows up against the wall, originally climbed the white trellis, but its vines are now sprawled out over the japanese maple and the otto luyken laurel on the right.
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I love the integrifolias and integrifolia hybrids as well so Sizaia Ptitsa is a great one I would recommend.
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Although not a huge fan of the type IIs, I must admit that Piilu is a great early season bloomer in my garden. I have posted pictures previously this year of mine and now it is even more covered in blooms than it was previously. As Karen pointed out it tends to be a shorter variety of clematis, but then again I treat mine as a type III clematis (which is why I never get double blooms on it) and this year it was whacked back to ground level and it is still going gangbusters and well over 5 feet tall. Mine is planted in the ground.
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Oh what fabulous pictures! I knew you all would be no help narrowing the pool! I think I'll probably buy maybe 3 or 4 this round and put the others on a wish list for later. I have planted several in shrubs and trees as you suggested flowerfan2. I like this approach since we're only allowed to have 4' fences in our neighborhood and I have only a few obelisks and trellises. I will have to scope out some more planting spots this weekend and place an order. It's looking like Huldine, Piilu, Duchess of Albany and Sizaia Ptitsa for this round but I'll probably change my mind a dozen times before I place the order.
Thanks for your responses and the inspiring photos, they're just beautiful!