I'll still say the Dickey deal was the worst trade in history, not just for letting Syndergaard go, but also d'Arnaud leaving and thus having a replacement level shitheads in Arencibia and Thole as the two catchers.
Dickey RA/9 WAR: 9.6
Syndergaard WAR: 18.8
Travis d'Arnaud WAR: 8.8
JP Arencibia WAR: 0.0
Josh Thole WAR: -1.0 WAR (in basically f***ing 1 season worth of cumulative games)
Let's not forget the negative value that Dickey was generally not fun to watch pitch, even when he was having a good outing.
Best trade though should start with landing Josh Donaldson, looked incredible from the get go and only looked better as time played out.