Nimbostratus
http://support.f5.com/kb/en-us/products/big-ip_ltm/manuals/product/ltm_configuration_guide_10_1/ltm_persist_profiles.html1184508
It's based on your need. I've typically used destination address affinity for outgoing traffic using a wildcard Virtual Server and a gateway pool to ensure the same gateway is used..
Source address persistence is a good choice when the traffic is client based, in other words, the requests are coming from different IPs.. It may not be a good choice if the traffic is sourced from... oh lets say a proxy using one IP..
