I use Spratt and Winkle autocouplers and electromagnets (from SEEP I think) on my layout, modified a bit as per this photograph which I put on old thread on the site.
http://www.rmweb.co.uk/community/index.php?/topic/50279-o-gauge-auto-couplings/page-6

Since posting the photographs, I've changed my method slightly: although my layout is end to end I can't really used "handed" rolling stock, ie - hook at one end, loop at the other, because I use a train turntable off stage. In the quest for 100% reliability I now fit loops to both ends of all wagons, half of the wagons also have hooks at both ends, locos only have loops. The snag with this is obviously that certain wagons can't be coupled directly to each other, but I have now achieved such good reliability that shunting is a real pleasure.

For my new Lionheart B set I pondered about how to do the couplers and I have fitted Spratt and Winkles, hooks only, iron wire droppers instead of 3 links, no loops as the outer ends of the set will always couple to a loco with loops. I have been able to leave the existing screw couplings in place, which was good as I don't want to alter the coaches unnecessarily. Hopefully the photos will make some of this clearer. The route for the passenger services only has gentle curves so was able to use the length of the Spratt and Winkle hooks to go right round the realistic model hooks and achieve reasonably close coupling. I've been testing the couplers today and they seem to work faultlessly. Result!