For us, it will be variant 2, but without stringers, instead the steps are fixed in the (solid) wall and on the corridor side only spacers between the steps ("Buchertreppe" ... is now more or less the standard model at Treppenmeister). I find this the nicest and most airy and would also recommend it to the OP, insofar as he even wants to stick to the variant with the staircase along the corridor tube.
However, I also find landing stairs sensible in many floor plans; I would then build them as concrete stairs with usable "space" underneath.