Nice one this, and they can be tricky to separate, especially in non-breeding plumage, and many are intermediate.
But this is why I think your bird is a Little:
If you look at how long the white forehead patch reaches towards the eye, you´ll see that it doesn´t reach over, and behind the eye, which it doe´s in Little
and in your tern.
Is that enough to separate the two you are thinking?
That upperparts is paler (usually darker than little in winter, the opposite), than Little and the rump and tail is grey we can´t see here, white rump and tail in Little, although Little breeding in same area as Saunder´s often has central tail feathers grey. Saunder´s usually has more extensive black on outer primaries, 3 (4) black, against 2 (3) in Little, which then would be seen on a standing bird as less black on outer primariy tip, as in your bird.