I have the GS...PAP2T...SPA2102..and who knows what else.

Even though I can go in have done my own programming, etc., I have chosen to let VOIPo do the configuration on-line by them.
Even though it goes against my basic nature, letting them control it has been flawless for me.

For some time now I have been using the GS502 and hope I'm not jinxing it by saying so, the service for me is as good as it gets...

I sometimes connect the PAP2 and this also works well...and my SPA2102 is a gem.

I use a separate router as I have never found a combined ATA/router or Modem/router combo to work very well. Just my experience. I will only put my ATA or modems behind my router and with port forwarding, I have smooth sailing.

Insofar as your desire to have unfailing service in the VOIP world, I don't think it exists. We are tied to the quality of our ISPs as well as the rest of the internet.