The [newer] Piper Seminole have Garmin G1000NXi avionics, before they were equipped with the G1000, some retrofits have G500, older ones have regular six-pack instruments. ATP Flight School uses them successfully.
https://atpflightschool.com/equipment/seminole.html
The Diamond Twin Star has the Garmin G1000NXi, not sure what the older models had.
https://www.diamondaircraft.com/aircraft/da42/
All in all both are really good airplanes, but the DA42 is a newer generation airplane, it is better built and with center control sticks (vs. conventional control yokes on the PA-44). Having flown both, my choice is the DA42, without hesitation. Good luck!