In Missouri the best law is really a combination of two adjacent statutes. 307.190 and 307.191
"307.190. Every person operating a bicycle or motorized bicycle at less than the posted speed or slower than the flow of traffic upon a street or highway shall ride as near to the right side of the roadway as safe, exercising due care when passing a standing vehicle or one proceeding in the same direction, except when making a left turn, when avoiding hazardous conditions, when the lane is too narrow to share with another vehicle, or when on a one-way street. Bicyclists may ride abreast when not impeding other vehicles."
I like that wording because it lets me decide where the safest position is. A lot of these Kansas City roads are substandard width, so I exercise lane control frequently.
"307.191. 1. A person operating a bicycle at less than the posted speed or slower than the flow of traffic upon a street or highway may operate as described in section 307.190 or may operate on the shoulder adjacent to the roadway.
2. A bicycle operated on a roadway, or on the shoulder adjacent to a roadway, shall be operated in the same direction as vehicles are required to be driven upon the roadway.
3. For purposes of this section and section 307.190, "roadway" is defined as and means that portion of a street or highway ordinarily used for vehicular travel, exclusive of the berm or shoulder."
I like this one because it clarifies that 1) the shoulder is not part of the roadway and 2) the shoulder is 100% optional. It also does not include any language mandating bike lane use.