Well at the lower levels you won't get that great of gp or exp. Once you get higher in combat, slayer level, and masters you will be getting better tasks and exp. But at lower levels its probably best to also farm herbs. I know yesterday i put toadflax herbs in the ge at min and the sold auto at max so that might be something to look into. It is up to you which way to go. All my combat skill, including range and a little magic, have come from slaying. I love the skill and I am so happy i finally got 99. After I get a few skills up i plan on going back and getting 15m+ exp in the skill. Slayer isn't the best or fastest way to gain combat and exp. If you think you should train another way then do so.