Forgot to post an update: stayed at JW and visited IC Landmark just to compare (asked for a small tour to show me rooms and the Club). I have seen the Club only in terms of layout, since I went really late and it was already closed: they just let me in for a couple of minutes. Cannot comment on offerings there. Design-wise the Club there is really impressive, more pleasing than JW to my taste. The rooms were the opposite: complete disappointment after the outstanding suite at JW. Since I have stayed after at IC Nha Trang, I can add that rooms there are much better as well.
As for IC Landmark, given its poor location and unimpressive rooms, can't justify booking a regular room, and booking the Club makes little sense at their price point. Thought to use Amb cert there at first, but Amb rates are insane. Sheraton looks like a total bargain, booked weekend there for August and perhaps gonna stay there.
P. S. If you got Gold or Plat with Marriott, go for JW, it's great.