OK, Thanks!
I would also have liked to hear from some more experienced US birders.
Now I will write you my opinion. I think it looks more like a Semi rather than a Little Stint – but I have definitely not set my to it, so any help from you will still be appreciated!
The sandpiper/stint was photographed in very bright sunlight.
The Bill: It doesn’t seem as thin and pointed as on little stint - it looks a bit blunter. This feature, I admit is not objective, and looking at pictures of Semi, they also often have bill appearing both thin and pointed.
The legs: I have tried to the bird in question out I Photoshop, and put it in together with a picture of little stint. The leg seems thicker and the knee much stronger.
Webbing: I know that the webbing on semi is very difficult to see. If you look at the second picture, the left foot does not show webbing, but couldn’t the be because what you actually se is the split between the hind toe and the long toes? I have the impression, that the shape of the split between the toes on the right foot shows webbing (maybe it is jus me really wanting to have seen a semi in Denmark???)
Length of wings: The wings does not reach tip of tail. I had an idea that this was an important feature for Semi.
Lower scaps: On the first picture, the light hits the bird, so that it is possible to se the markings on the feathers rather well. Especially the rear of lower scaps shows "anchor" marking. As for the rest of lower scaps, the have some kind of markings at centres no solid as in little (question, how big is variation on little?)
Upper scaps: on Little stint edges should be: for lower part of feather white and for upper part of feather warm buff. Solid centres as in this bird, seems normal for Semi (only experienced this form pictures found on the net).
Coverts does not look solid, but dark centred getting paler and paler towards the sides and ending as a pale whitish tip to coverts.
V-marking on back obvious, but quite narrow: in my opinion only half the width as little stint. It seems that semi normally does not show that much, but also for that part, I have found pictures of semi on the net with similar.
Supercilium: At first I thought, that the supercilium was all wrong. The first pictures of semi that I consulted, had a faint and broken supercilium. But variation on Semi appears to be much bigger than in little stint (which by the way varies a lot, especially in adult/2K plumage!). And my conclusion is that the supercilium is good for Semi.
OK enough for now – hope for some good advice and explanations.