"Mind you the number of people who have told be that they have one but have never used it because they can't work out what to do with it are legend." Count me as one of those guys. Even have a few 'Cobblers' for it. I do however, like demonstrating my $29 tiny computer surfing the web. But I've never done any physical computing with it.
I still like DUE. I hope Arduino continues to develop it. They left some spare I/O and the Ethernet on the table. Hopefully, they break that out in a future versión one day. Wish Atmel had given us a Little bit of epromm memory with it as well.
YUN, Galileo and TRE look complex and expensive.