Tester please expand on your arguments as I am not sure what you are trying to say. H.323 doesnt scale, because its old. Age also means maturity, which also means they vendors have put in time to scale it fine.
Also the ITU is finding various ways to get the “protocol” to scale i.e. Annex E. To date the largest VoIP networks are H.323 based. It also has things that SIP doesnt such as mechanisms to keep call state.
Also im not sure what you mean by convergence signalling? Are you saying that the fact that SIP was created for session management rather than “just multimedia” that it is more flexible for applications other than voice and video. If that is what you are saying then yes, SIP does do that. 🙂
My point is SIP and h323 are just protocols. No matter what anyone tells you there is no “better” protocols, there are just better ways to do what you need done.
Since your application is PC to phone apps, it leads me to question a couple of things. Are you building from scratch? If so, it may pay to go the SIP route, that way you can figure out a killer app that can leverage the intelligence of the PC and the flexibility of the SIP protocol. If you want to go with stuff thats already out there… it will depend….do most of your users have the proper client support of a particular protocol.
IMHO there is no better protocol, but there are protocols that solve some problems better. Define your problem and then weigh the ability of the protocol to be extensible to your applications.