Typically routers always select the path by examining the prefix length of as network entry, with the chosen path being based on prefix length. The longest prefix length always being preferred.
The logic can be used to influence path selection in BG. Path attributes can be used to influence traffic too, but there may be a neighbour that chooses to ignore those attributes.
The best practice way of advertising BGP routes for maximum compatibility is for every peer connected to the BGP edge to advertise summary routes, then selectively advertise more specific routes out of the preferred BGP router that traffic should be received on.