I have ridden all three as well.
1300 GS - I have ridden this several times, once for a few hours. I find it too small, too harsh a ride and overly complicated. It feels to me like I have been disenfranchised by BMW. I wanted another GS and had every intention of buying one with my expectation being more of the same with a bit more speed. It was a massive disappointment to find that to me, the bike had lost its GS-ness.
KTM - I actually spent some time on the Super Duke GT 1390 and I thought it was fantastic. Brilliant suspension and fabulous power delivery. I would probably have bought one were it not for the slightly precarious state of their business. I also have reliability concerns with KTM and don’t want to get stuck in the Dolomites with a broken bike. The looks aren’t quite to my taste either and it bugs me that you have to pay extra to unlock features that are already on the bike. Very nice machine to ride though and I can see me owning one at some point.
Multistrada V4S. Well I bought one so I must like it? Yes, I do. The handling is amazing and it looks and sounds great. And the brakes are unreal. As said above, I am yet to experience the engine properly as it is limited to 6k rpm for now. But it is not perfect. I am irritated by the lack of space near my boots and have to shuffle around more for the gear lever. I agree about the wind protection although it is actually better than I was expecting. The panniers seem flimsy too but I am coming from the BMW adventure ones so that is a natural view to take. It is way too early to give a qualified opinion on it but what I can say is I am really glad I bought it and it makes me smile when I walk in my garage. It is very well designed in terms of user interface and having ridden it in the dark last night, the lights and backlit switchgear are excellent. Best lights I have ever had on a bike for sure. And one last thing. It has tech in it that when the front registers a bump, it sends a signal to the rear suspension to anticipate the same. I thought this sounded like a gimmick but it actually works and is really noticeable at any speed! The front hits a dent or a hole and you feel nothing as the back wheel passes over it. Very clever. Time will tell if I love it as much as my last GS1250 but the signs look good so far.