Switching between USB power and single alkaline battery
Both the boost regulators you have listed have an EN input.  This is used to enable or disable the regulator, and can be very simply controlled by the USB's input power:







simulate this circuit &ndash; Schematic created using CircuitLab

Under normal battery operation R3 pulls the EN pin high, so the boost regulator is enabled.  When you connect the USB current flows through R1 and turns Q1 on. this pulls EN low.  R2 is used to ensure Q1 switches off when there is no USB connection allowing R3 to pull EN up again.

You may want to still keep the two diodes to prevent any back-flow of current through the regulator that isn't currently in use.

Note: I chose the resistors with ball-park figures. You may need to tweak to both ensure the EN pin gets the right voltages / currents to activate, and keep your quiescent current through R3 as low as you can while the USB is connected.