I will say that this has been the most entertaining run from Chris Jericho since his 2010 run. I enjoy that he comes in and out when needed (and wanted, of course), and that while he is here, he does the house shows and everything too. I think for that he really does deserve credit. At his age and the length of a career that he has had, Jericho is performing fantastically.
But...
AJ Styles, man. Yes, Y2J (and Kevin Owens) have been carrying Raw on their backs since the brand split. Rollins, Reigns, Strowman etc. have done their part, and are arguably in better positions now than before, but I think Jericho and Owens were doing fantastic things together. But despite all of that, AJ Styles has had one hell of a debut year in WWE. There is no need to go through his accomplishments, we all know what they are. And he has arguably made more of an impact. Jericho has had a great year no doubt, and while he continuously entertains me with his constant reinventions, we know what Jericho is capable of. For me, I knew what AJ was capable of before WWE, but until you see what he actually does in WWE, you cannot guarantee that crossover. Right now, AJ is so damn over. He has done such a fantastic job on SmackDown that for me, he edges Jericho.
I think The Miz is also a good shout. His recent stuff with John Cena has been the icing on the cake for WrestleMania 32-33 period, and I fully expect it to continue on Raw (people need to stop panicking). Like Jericho, this was a reinvention of something we all knew existed, the difference being that this has probably been the best run of The Miz's career.
Overall, I'd give AJ Styles the number 1 spot. Jericho probably comes in at 2 because he's taken on a very significant role on Raw admittedly, which is more than can be said in his runs since his 2012 return. Then again, as some posts have said above, can you honestly name many significant matches he has been in? Regardless, Jericho has been fantastic. But AJ Styles.
And this is all coming from a MASSIVE Jerichoholic.