For the 737-3/4/500’s, we used to use flap 2 on approach, before the flap-speed schedule was changed in year 2000 to increase the block speeds of the lower flap settings. The schedule below 53,070kg was: Flap up - 210, Flap 1 - 190, Flap 2 – 180, Flap 5 – 170, Flap 10 – 160, Flap 15 – 150. So if you wanted at fly at 180kts you used flap 2.
It was considered good practice to work your way down through every flap setting and be within 10kts of each schedule speed before selecting the next stage of flap all the way to landing flap to reduce loads on the flaps.