Joining network groups in my opinion has a greater ROI but you must participate in the network groups, joining them and not attending the functions is useless.

Also, networking groups have a higher ROI but you are in front of a much smaller group. We joined BMI and each meeting there's usually about 20 people at breakfast, we all know each other so referring each other business is something we do.

Buying advertising puts you in front of much larger numbers of people who you aren't having breakfast with each week, so in my opinion it's important to do both