No need to limit this to the BW/Q.  Any portage anywhere can be thrown in as a favorite.

There's a nice one in APP going from Shah to Misty.  Starts with a steep up, get that out of the way early.  Long gentle decline to Misty.  Nice transition from high-ground to a swamp edge to the lake proper.  Near halfway is a grove of cedars that blocks a view to an old tote road, long since decomissioned & overgrown.


Temagami has an intersting one on the Lady Evelyn R., N Chanel.  Going upstream it's the 2nd one from Sucker Gut.  Not long, but follows a set of waterfalls.  About halfway is a 10-15' cliff.  A solo tripper might want to rope the canoe up.  There are solid foot-holds, but the cumbersome canoe + the wrong wind would be interesting.


Dickson/Bonfield in APP for bragging rights.  5.3km/1000 rods - mostly it's long with a couple tricky ankle twisting sections.  It's the portage that broke me, double carry, I got fed up ~500m from the end and camped on the trail at dusk.  Finishing the next morning I just laughed at myself for getting so close & yet being so far.

The portage around the last falls leading out of the pot hole section of the Kopka River- you can hear the river going down, down but the portage stays up until.....

That simply an amazing portage, Solus.  Can't imagine ever doing something like that.

For me, I still recall the feeling I had on that portage from Crooked into the SW arm of Argo.  Heading gently uphill through old forest was like going back in time.  The gound was so soft, the air so damp, and the pines so old.  And then after hitting the peak and heading down to the granite slab diving into that unique tint of Argo's water....I'll never forget it.
 

Any portage where the blueberries are thick and ripe is my favorite.