beam causes the particle the multiply itself based on the direction - making it kind of like a "train" i guess. Streak stretches the particle. For a smoke, or rocket smoke, you don't really want to set a velocity speed. If it was a spark, or a blood splatter, then you would want to use the velocity. if you want to spread the particles on creation use:
effect(smoke,1,vector(my.x+random(16)-8,my.y+random(16)-8,my.z+random(16)-8),nullvector);
