WOW! Tough question. I own both of these guys in a league with similar settings.
I am always worried about Borowiecki's icetime/opportunity. Right now he is getting prime (for him) minutes. He is PIMS, HITS & some SOG/BLKS. Boychuck is a multi-cat stud when healthy (and younger). He is great for SOG while providing good HITS and more BLKS. Neither of them are the ice to score.
If this were an endurance race I would pick Boychuk easily. But we are talking the rest of the season. Borowiecki looks to be a lock* to be a top 6 Dman for the remaining 22 games. He is playing close to top 4 minutes over the past four games.
FINAL ANSWER: Mark Borowiecki - I want 22 games of a 15+ minutes per night Borowiecki more than 20 minutes a night of current Johnny Boychuk.
* may not be a lock