I have duku, longkong and duku langsat fruiting in my yeard just about every year and frequently get to try langsat also. Last season I sampled a large fruited sweet Indonesian variety that appears closer in form to langsat than anything else.I have been asked quite a few times which would I rate the best fruit of the ones I have tried. If we rate them on big fruit, thin skin, sweet taste, low latex in skin, few seeds that get in the way of eating and juiciness as positive characteristics then some are sure better than others.
I would rate the best varieties as longkong ahead of duku of all types I have tried and just ahead of the large Borneo langsat (not true langsat) with duku langsat a clear winner. It just tastes better and is more juicy with a range of other positive characteristics. Crops may not be as heavy as duku and longkong. It just so happens I picked some off my tree today and here they are.