That is interesting. We use vovida stun and have not experienced any problems at all. What exactly are you referring to?
MyStun is terrible, IMHO, and VOCAL is a dead project, so neither are good choices for our company.
Yes, vocal is dead, but pretty much so is also the STUN protocol... In my experience, a combination of STUN, ser sdp rewrites (incl. direction=active) and rtp proxying covers pretty much everything and reduces your rtp proxying to a minimum. Yes, you have to test each device behind different NAT types to make sure that the behavior is correct. A public list of device experiences with a such "keep RTP to a minimum, but support devices behind NAT" setup should be of interest to many. Anyway, I agree. It's too bad that no maintained GNU STUN server is available. More and more devices support stun and it works amazingly well in most cases if your setup is correct. It's just that NAT is a problem that is difficult to get your arms around and if your ser.cfg is not correct, you have problems and end up with either your approach or proxy everything... g-)