Bouma hits hot streaks where he plays his game really well, and at other times falls off the map and is either invisible or can't move the puck. Right now he's in a cold streak.
If Lazar is anything like Bouma, he's in a hot streak right now, and hungry to stay in the lineup. He hits, he cycles well, he honest to God just plays basically how Troy Brouwer is supposed to be playing. And I get the impression he's already friends with everyone on the team. Based on how he's played in the four games we've seen him, I'd put him in over Bouma.
However, I think we need the physical and shot-blocking elements that Bouma brings against the Ducks. I agree that we shouldn't be trying to beat them at their own game, but we need to be able to respond. Last time we played them, we got spun in circles because we couldn't play to their level. Bouma is one of the few guys on this roster who can.
tl;dr against any other opponent, Lazar. Against the Ducks, Bouma.