We are Plat Premier in Marriott, soon to be Titanium in the Bonvoy program (the name still baffles me), Diamond with Hilton and Platinum with IHG (which gives us practically no benefits besides upgrades). Our fav travel destination is definitely the beaches in Asia and South America, but even with the joint effort of SPG, we faced this problem with Marriott, is that their properties are very centralized. Take BKK for example, we don't want 10 properties within 0.2 miles radius in Sukhumvit, we want options to be near night markets or other districts near central world mall, so this is where Accor comes in for us, we only justify booking with Accor when they are actually cheaper than hotels.com/booking.com when they have those private sale. So like most had mentioned, it depends where you travel, if you can find reasonable properties in your path, go ahead and be loyal. If not, there is always, hotels.com.
For what's worth, Marriotts in the US are not worth the hype, they look great as a branding perspective, but you get very lousy recognition in the states because they are flooded with elites here. Think a JW in downtown Chicago, you can have up to 10-20 plats check in at any given time day, there is only so much free suites inventory you can give away. And the lounge is small, usually packed with families. Overall, you will always get much better perks in Asia.
I'm only "member" with Accor, but this is just my 2 cents with Marriott..