I’ve only dealt with 140mm Monty’s and 150mm Black Widow’s, but based on that I would have to say that the Monty’s will rake out just a little more than the BW’s. Also, the edges on Monty’s are rounded which will let Active Ankles or body parts slide off more easily without catching and causing a blood letting.
I also think the Monty’s are stronger, but you have to make sure they are pressed on the axel real good.
The Montys are going to be stronger. The Black Widows are good for XC muni and Cokering, but I wouldn’t do drops with them.
I used the Black Widows on my Pashely back in the old days when I was using a 2.1" XC tire and doing XC style riding with no freeride stuff mixed in. Never had any problems with the Black Widow cranks, but I wasn’t doing any jumps and drops at that time.
The Black Widows are very straight. You can get unicycle.com to confirm, but I would be very surprised if the Montys didn’t have more rake.