Shapiro has baggage. He's not great when it comes to Palestine (no, not because he's Jewish - Bernie Sanders is Jewish and has not misstepped nearly so badly). He's called pro-Palestinian protestors - who, like them or not, are largely young liberal college kids that Harris needs to vote for her - equivalent to the KKK, and he wrote an op-ed years ago coming WAY too close to calling all Palestinians mindless savages. Biden misstepped badly on Palestine - Shapiro doesn't seem inclined to do anything but double down on that front. Also, he wasn't awesome when a subordinate was accused of sexual abuse.
BUT, he has the possibility of shoring up PA, which is potentially very important. I would also enjoy him mopping the floor with Vance, but that's the petty brat in me.
Walz is more progressive, which could run a risk with more moderate voters. But he could also continue to raise enthusiasm with younger voters who tend to need to feel enthusiastic to show up, and I think he very much speaks to white blue collar workers (because if he didn't, he wouldn't have won Minnesota).
