Suppose a report appears in Muslim, has multiple substantial routes, is well known below the level of tawatur, and has corroborating indications strong enough to yield inferential knowledge. In that particular comparison it may be preferable to an isolated report in Bukhari that lacks comparable added support.
Claims about multiple routes must be checked for shared bottlenecks, severe weakness, and actual transmission independence. Mere popularity in everyday speech is not technical corroboration.
Rule of preference: presence in either collection supplies major presumptive weight, but strong independent support can matter in a concrete comparison.