Both great speakers IMO, but very different. LS3/5As are truly superb on acoustic music and have astonishing abilities when it comes to creating a soundstage. If you mainly like jazz, string quartets, female vocal etc they may be amongst the best speakers you ever get to hear. They need to be away from walls on high-mass stands and ideally driven with a very nice valve amp. Kans are the polar opposite, they need to be hard against a solid rear wall, on their dedicated open-frame stands and driven with a good fast and punchy solid state amp. They are not great tonally, but superb fun on rock and pop music and are a wonderful speaker if you are stuck in a little rented flat or whatever. If you like classical music forget them as they can’t do the scale and are just too odd tonally.
I really like them both and owned Kans for well over a decade driven with various Naim amps right up to 135s, though given how my musical tastes have changed I’d now pick LS3/5As out the two now. I actually have JR149s for my mini-monitor fix which represent a very nice mid-point between the two being punchier and grippier than 3/5As and having far better tonality and soundstaging abilities than Kans.