I forgot to mention that all three of these companies couplers are completely plastic except for Maerklin's which are mixture of plastic  and metal.  I have done European model railroading for many years and I have never had one break.  For ease of uncoupling, I recommend either the ROCO or Fleischmann couplers.  To uncouple, simply lift one of the two coupled cars up.

There are several different types of NEM close couplers.  Fleischmann makes "Profi Couplers", Maerklin makes their own and ROCO has their version.  I use Eurorailhobbies in Canada, there are also several other dealers scattered around the country.   Just do a Google search for ROCO model trains or Maerklin.  Maerklin are AC trains but their close couplers work on either DC or AC trains.

A few years ago Walthers made a Mainline UP RS2 model.  You might find one out on EBAY.  I have one and it is a good runner.