I'm assuming we'll see a $399 PS4 Pro holiday bundle before a vanilla $349 SKU.
As for the numbers predictions, it can probably easily be boiled down by looking at production numbers and availability of the respective consoles. I don't see PS4 Pros flying off shelves unless we see some great bundles. I would expect to see more shine behind the XBOX as the newest/bestest, so sales really depend more upon how many units MS ships than anything else. If stock on those is readily available, I'm not sure what to think about the market reception.
It's no shocker or huge prediction that Sony is going to sell far more PS4 slims than either and probably even both combined.
The XBOS stands a good chance at selling more units than the XBOX as well if we're looking at a $249 or maybe even a $199 XBOS compared to a $499 XBOX.