this is mainly down to what you allready have in your army.
kommandos can ambush, but once they have, they are sitting ducks, your paying 10 points per ork as a sacrifice for a single attack, as once you ambush a unit, you will either be brought down in
CC (slowly) or shot to death.
stormboyz are a little more expensive (2 more points :O)
but thier extra movement helps alot, then can fly into a combat, kill a unit, then run off and hide behind cover.
ok, so you may lose a few on landings, but thats the ork way of life.
also, dont have to worry about them running off as zag will execute one to stay in the fight
all in all, i'd take a nice large unit of stormboyz, high movement, early assults and dont have to worry about being able to get out of the
LOS quick enough.
Edit: spelling.