I am an architect from WSO2 - mostly leading WSO2 Identity Server. I am trying to be not bias as much as possible :-)
Both products bring you a comprehensive Identity Management platform - having support for SAML2, OpenID, XACML 3.0, OAuth 2.0, SCIM, WS-Security standards.
Few unique features that I would like to highlight on WSO2 Identity Server are...
- Decentralized Federated SAML2 IdPs (http://blog.facilelogin.com/2012/08/security-patterns-decentralized.html)
- Distributed XACML PDPs
- User friendly XACML PAP wizard
- High scalability (We have a middle-east customer using WSO2 IS over an user base of 4 million for OpenID support.)
- Cassandra based User Store ( To be used over 800 Million user base by one of our production customers)
- Light-weight and Very low memory footprint. The stripped down version of WSO2 IS can be started with 64MB Heap Size and the standard versions runs with 96MB Heap.
- Highly extensible. The architecture behind WSO2 IS is highly extensible. You can easily plugin your authenticators, user store, etc...
- Support for multi-tenancy.
- Suport for multiple user stores (AD, LDAP, JDBC)
- Interoperability.
- Part of a proven SOA product platform provided by WSO2.
Also, we are planning to add support for OpenID Connect this year with a set of improved Identity Management capabilities.
You can also read more about WSO2 Identity Server from http://blog.facilelogin.com/2012/08/wso2-identity-server-flexible.html
You will not get an unbiased answer from me for your question :-) "Which one would be the best amongst two ?". You will aso get answers from Forgerock and other folks here. Best would be to evaluate and decide.