Hey GermanGal, basically all networks have their advantages and disadvantages. But like you said for the most part, many networks carry a lot of the same offers. When at that point, it basically comes down to who offers the better payout and has the better converting creatives.
Also, networks use all different types of tracking systems to track leads/sales. This can make a difference in you monthly commission big time. Some tracking systems fail to track leads every now and then, but they could be big leads and could end up losing you money. So investigate how the network tracks sales/leads. We ourselves use the popular DirectTrack.
Another big factor, is basically service. How accessible, friendly and helpful are the affiliate managers with the network. It's nice to be able to get in contact with your affiliate manager whenever you have a problem or question. Many networks take up to a week to respond to an email and don't supply the correct phone number to speak directly to your account manager.
So basically, you are correct in your thinking that many networks are the same, but at the same time, you will find the benefits of other networks over others all the time. It's just a matter of you joining and checking them out. Also, work of mouth helps a lot too. So if you are interested in a certain network, ask around for opinions.

Jon Lyons | Affiliate Managerjon.lyons@fluxads.com
AIM: FluxAds |
www.FluxAds.com"Make Every Impression Count!"