For those thinking this sounds like a full gone conclusion...read on.
Whilst booking the MO in Jakarta, they asked which hotels I has stayed in the city and I mentioned the J.W. Marriott- they scoffed that it was in a totally different class. So, were they right? Having completed my stay, I don't think so.
I must say that the service at the MO was outstanding and possibly had the edge on the J.W. (they genuinely try to do all they can to make your trip as pleasurable as possible). That said, service at JW's in Jakarta and Bangkok is also fabulous (very much in the same league) with Grosvenor House being my only disappointment).
The exec lounges were remarkably similar although I must confess that I expected more from MO. To my mind, the lounge at the J.W. in Bangkok is the best around. 1-1.
I was upgraded to large room similar to a junior with MO and a suite with J.W. so the rooms were fairly comparable, one with a better view, the other slightly newer.
If cost and loyalty was not a consideration, I would struggle to choose between them but may opt for the MO. Taking cost and loyalty into account- you can guess the rest.