#4 Impact Wrestling
Much like New-Japan of America, Impact is a company trying to gain footing. It's obviously a different scenario, since NJoA is starting almost from scratch while Impact has almost two decades of history behind them. Impact also has a strong core roster and is already gaining momentum with their parent company, Anthem, purchasing AXS TV and putting the show in primetime on Tuesday nights.
Regardless, a mind like the one possessed by Joey Mercury could prove to be crucial to the ongoing success of the brand. It gets you another former wrestler in a position to teach younger talent, and the company gains a man who can be a secondary locker room leader (behind whichever current Impact star is considered the locker room leader among the active wrestlers).
Mercury doesn't appear to be in it for the money, but the love of the business. Impact has more money now than they have had in a long time so they would be able to offer him a good contract (likely far better than what he was making in his most recent endeavour), which would be another incentive to join the rebuilding brand.
He's also a good guy to have around when and if Impact becomes a touring company due to his many years travelling the country and the world with WWE, Ring of Honor and more.