Ultimately, you need to create a list of pros and cons, that you need/want.
I think AJ's are very discrete, but I wouldn't use them because they don't have
the delayed uncoupling feature. I've used Linc's, which are also quite discrete,
but again, don't have the delayed uncoupling.
I don't like using Kadee's on British goods stock, it just looks wrong!
Also I'm not keen on all the types that are different each end, which means all
the stock has to face the same way, and more issues with using a turntable!
I'll admit my preference is for S&W, as the best compromise (for me) between
ease of fitting, flexibility in use, and looks.