Nets that are routed sub-optimally are often the result of incorrect timing constraints. Before you experiment with router settings, make sure that you have validated the constraints and the timing picture seen by the router. Validate timing and constraints by reviewing timing reports from the placed design before routing.
Common examples of poor timing constraints include cross-clock paths and incorrect multicycle paths causing route delay insertion for hold fixing. Congested areas can be addressed by targeted fanout optimization in RTL synthesis or through physical optimization. You can preserve all or some of the design hierarchy to prevent cross-boundary optimization and reduce the netlist density. Or you can use floorplan constraints to ease congestion.