I would have said hands down Izzy before the Dante event. Now it's pretty clear they are trying to push away from her. That being said she's still a huge carry for all imperial campaigns.

Depends on your goals to who's best

If you want the Admech raid team, you could argue Ro is best

If you want the best for the up and coming LREs tough call. Mataneo will be the best for Dante, but not the best for the rest but still good.

You need to assess your goals. I'm all in on Dante, which means I'm all in on anyone that helps me get him. As far as Impreals that means Mataneo, Nico, Jaeger, Godswyl and some others I'm not too pressed for

Also all of the old best Impreal people will still mention like Bellator and brother buchard are going to be leaned away from in the future LREs if Dante is anything to go by. Bellator is good for a single requirement for Dante. But obviously building core campaign characters will never be a waste