Having watched the original Terminator and Terminator 2 recently, they should have ended it there. There was not much need for a 3rd movie, because T2 ended things fine. Both the T-800 and T-1000 melted in the steelworks, so no evidence. John and Sarah probably grabbed the T-800 arm left behind and threw that in as well. Miles Dyson's work and the whole of Cyberdyne were blown to oblivion. And it closed out pretty good, to the point i struggled to figure why a 3rd movie was required.
Salvation however, that was different and it was ok. Should have been a heck of a lot better, but there we go.
Genisys, that had promise but the story was the confusing part.