Depends a bit on alien tech level, enemy density and the map itself. In long war rebalance you get a preview of which map you'll play on before the mission starts.

Very early on 1-2 rocketeers can guarantee a victory thanks to the power of the rockets. They fall off in the mid game though. On swarming abductions I'd always bring a rocketeer because you're bound to hit something and because you're often under high pressure to immediately clear the area next to the landing zone before additional roaming pods patrol into you.