How we cite our quotes:
Jason: were you [Medea] living at the world's ends,
your name would not be known. […]
Oh, to me, houses crammed with gold, […]
are nothing with no name. (62)
Jason seems to think that his having made Medea famous somehow makes his betrayal OK. However, Medea never demonstrates the same need for fame that Jason finds so valuable. This weakens his argument greatly
Jason: I wanted above all
to let us live in comfort, not be poor (62)
Jason doesn't seem to see his actions as a betrayal at all. He contends that the only reason he married Creon's daughter, was to provide his family, including Medea, with a better life. This is probably his most credible argument, though the idea is alien to most modern audiences.
Medea: Go, my sons, into the halls of wealth;
down on your knees and beg her –
this new wife of our father's (161)
Medea could be seen as a traitor as well. She's purposely involving her sons in a plot which will make everybody in Corinth want to kill them. You might say that her betrayal is far worse than Jason's.