Ditto to that. I've only flown the Duchess, but made my decision based on advice from people who have instructed on both.
Everyone's different, but I found the Duchess a fairly easy transition from a complex single (Sierra). It's very very easy to land, and stalling is a non-event.
I'm sure the DA42 would make life much easier for the IR, what with a single lever, glass cockpit, a/p etc, but as has already been said, you'll be laying the foundations for your future career. If your first airline assessment is in a clockwork-dial sim, I suspect you'd find it harder coming from a DA42 than a Duchess or Seneca.