Omega is definately the way to go. I worked with the same chapter for about 10 years and the difference between when the chapter collected dues and with Omega collecting dues is incredible. The chapter based their budget on 85% collection, but was only getting 65-70%. With Omega there has not been a semester that is has been below 95%. The first semester we only had two women we did not collect from by the end of the fall semester (of 100+) and they paid by the start of the next semester.
I will tell you that it isn't cheap - but the more you bill through them the less it costs you. Of course what they bill you is just chump change compared to the extra that they collect for you. We figured in $40 per person (dues were about $550-600 for initiated members) per semester to cover it. You can do the math on that one.
They allow check by phone, mail and credit card payments. Bills can be sent to parents (if they are responsible) or to the member (if they pay their own). You can also keep track of info (phone numbers, email etc.) for ease of contact when members become past due. Depending on what your national organizations collection policies dictate, they will set that up as well (how long a member has to pay before suspension).
It makes it easy for the chapter treasurer and financial advisor to see where the chapter is at at any given time. Funds are deposited directly into the chapters account and can be put into different accounts (rent, chapter etc.).
There isn't much I can say bad about Omega except that you have to be sure to figure into your dues what their fee will be per member each semester so that you don't over budget. Their account executives are really helpful and quick to respond.
Can't think of anything else!
