Hi Noel
I have been using kadees for 25+ years with no problems. There is a vast range of different types to choose from, including different lenghts and heights. They also offer a variety of uncouplers, which can be fitted between the rails or underneath the track out of sight. There is even an electromagnetic one. Kadee have an excellent web site.
I have no experience with Spratt and Winkle or Dinghams, not sure what type Dinghams are actually. Then there is the question of can your coupler of choice be easily sourced.
A good idea would be to have a look at a couple of exhibitions and see how the various couplers work on in an actual working environment. Nothing like the pressure of exhibition operating to weed out the non performers.
One final thing, no matter which type you eventually decide to use, the reality is that there may/will be some degree of modification required to your models.
Until you gain experience with converting your rolling stock to a new type of coupler, I would advise using rolling stock that, if it gets damaged will not cause the same grief as a new expensive item.
Cheers Manfred