Lean D for now. Democrats would be incredibly stupid to take this race for granted, and I believe there is a lot more "upset" potential here than in PA. Running a more "Trumpist" wave insurance candidate and not some random boring "generic Republican" seems like the best option for the GOP in MI IMO.
That being said, I think there is an 80%-85% chance that this race is a very easy double digit win for Stabenow and maybe a 15% chance or so that it goes down to the wire. Nothing in between. That's just my gut feeling, and I could be wrong of course.
Pennsylvania's more likely to be a loss for Democrats, since Casey never seems to take his opponents seriously, and if Barletta gets in he well could lose. As for Stabenow, it would probably take Schuettte deciding to run here instead for Governor for this race to be seriously competitive. In that scenario I'd give Stabenow a slight edge, but it's definitely possible she'd lose then.
