They all can/will be competitive with the right setup or driver so to look at some of the other factors for each...
B4.1 Pros: Cheapest, widespread. Tons of parts out there. Tons of cheap used ones out there.
Cons: Low fit/finish out of the box, kind of agricultural. Very made-in-China, not the Associated someone who last raced in the 90's would remember.
22 Pros: Can go mid-motor out of the box if you're racing carpet, astroturf or a very, very high bite surface.
Cons: Check local parts availability - some stores just don't stock much Losi anymore due to them being part of the Horizon distributorship corporate family. Also, see if anyone in your area who is fast is running one. By me, many have been shelved.
RB5 Pros: Best fit/finish out of the box in the 1/10th OffRoad world today. Made in Japan rather than China and it shows. Hard to setup so it won't work at least ok.
Cons: Expensive, even worse parts availability.
Durango Pros: Nobody else at your local track will likely have one so if you get it hooked up, you could have a bit of an advantage for a while.
Cons: What some call innovative, others will call quirky and the "pro" for the car may wind up being unachievable. Worse still for your local track just having parts on the shelf.