I would think Bittrex is much more likely than Poloniex at this point. PBT is a Waves-based token right now and Bittrex already lists Waves. I'm guessing it will be at least a few weeks before we'll see it though. I think they've said they will wait for the final distribution in 3 weeks before having it listed anywhere else. It will be interesting to see what they announce in the coming weeks.
You're right! Bittrex already has WAVES, is much more viable than Poloniex, and lately people are migrating to Bittrex, just check the current volumes of negotiations, regarding PBT, what is the expected price per token?