Having worked in both Avaya Interaction Center (AIC) and Genesys, I would like to compare them. Please note that these are my personal opinions and you should consider your business needs to select the product.
Avaya Interaction Center (AIC) seamlessly integrate with Avaya EPABX and would be the first choice, if you have Avaya end to end solution in your environment.
If you have any other environment (Nortel, Siemens etc), you should go with Genesys call center solution.
I feel that Genesys routing is better than Avaya (even the user interface IRD vs workflow designer). Genesys Routing solution have more options and features to select the target than Avaya. I am particulary impressed with Genesys cost based routing solution (from version 7.5 onwards). To get more details about cost based routing, please refer to my blog.
As always, you will find the discrepancies in the call center reports (generated by EPABX) and call center applications like Avaya OA & Genesys (CCPulse+).
Avaya reporting system (OA) is web based and is preferrable.
Genesys have ICON to get mroe insights about your customer.
Avaya recommends only particular version of Java (even though latest versions are available) for their solution installation. While integrating with third party products like Siebel, it is better to check the pre-reqs of both the products.
I will be adding more in this blog as I further dig into each products.