Gustavo,
Authorize.net is definately the better of the two as it has a more complete API. However, it is missing the ability to refer to transactions by your order number. The importance of that is dicussed in the ecommerce status?
thread.
Nevertheless, I think that Authorize.net could be a decent replacement for Cybercash as long as you are aware of its limitations. Especially for smaller ecommerce sites like the one I'm working on.
I will start working on an integration between Authorize.net and the ACS 4 ecommerce module in a week or 2. If you have any questions post them on this forum.
