[SR-Users] Kamailio design that needs one b2bua

Hello there, I'm designing and implementing a kamailio solution for sip routing between several softswitch based on prefixes. IIn this setup i will need an b2bua in order to do topology hiding and also to make transparent the call transfer between phones registered in kamailio and softswitches(that doesn't support very well REFER messages). I was searching what solution should I use and I found 3 opensource solutions that for me seems to be acceptable: Sems. Freeswitch. Opensips with module b2bua. Based on your experience and contemplating the stability, performance and support, what is the solution that you advice me ? Thank you for you time. Anthony