I'd plump for the PA44. There's a flying school not too far from here that uses the DA42. From what I've heard there are issues around engine failure procedures. The only way to simulate an engine failure is to close the throttle unlike on the likes of the PA44 where this would be accomplished by a mixture cut.
When the throttle is closed the gear warning is triggered on the DA42. The student gets to equate the gear warning horn with an engine failure and any genuine engine failures aren't always immediately or correctly recognised. The student starts to become immune to what the gear warning is actually for and there is a real risk the warning will be ignored when attempting to land with the gear up.
Also with a mixture cut simulated failure, all engine indications are the same as for a genuine failure, (with the possible exception of the fuel flow) whereas closing the throttle to simulate the failure results in engine instrument indications that are contra to real life.
For me the DA42 introduces too many negative transfer opportunities for a student