I believe paid advertising is best. There are many different options out there, but the main benefit I have seen is being able to target your advertising to try and attract those individuals who are willing to spend money.
Paid advertising also frees up your time to do other things, like communicating with your downline more often on a personal level, so that you can teach them the same things you are doing.
If you can afford it, paid advertising is the way to go.
