The thorny issue of coupling systems is one that troubles most modellers most of the time. Given that the prototype has more more than one system there never will be a 'right' answer - it really is a matter for the individual to decide. The only thing you can ultimately be sure of is that any self-appointed expert holding forth on the exclusive use of brand X is most definitely wrong.
Regardless of which type I've been hooked on, as it were, over the years, one I've always had a lot of time for within rakes is the version of the prototype instanter coupling manufactured by Smiths. Merry-go-round trains such as this one are rarely uncoupled on most layouts, so any fiddliness inherent in these tiny devices that might put you off ceases to be a worry. I tend to hook the vehicles together as I place them on the track and that's it. End vehicles can have whatever coupling you want, while within the rake these little things give nice, close coupling between vehicles.
Highly recommended at under a quid per wagon, the Smiths product code is LP2 for a pack of four pairs and they're widely available from model shops.