Softball weigh around 180 grams or that would be 0.18 Kg. Basketball usually weighs around 22 ounce or 0.6 Kg. To compare the momentum of the two ball we have to use the formula of momentum which is p = mv. m for mass and v for velocity. let us assume both ball are travelling 2 m/s).
Softball. p = mv = (0.18 Kg)(2 m/s) = 0.36 Kg.m/s ( smaller momentum)
Basketball p = mv = (0.6 Kg)(2 m/s) = 1. 2 Kg.m/s (larger momentum