Nylander is the more talented player, but I think that was probably true last year as well. For Nylander the issue has always been consistency and effort. I like hearing that he was pissed off about the way he was playing, because it means he's paying attention.
Who is "better"? I would say it's a coin flip at the moment and could change night to night. JT plays a harder position, he rarely takes a night off, and has the burden of captaining the team. Nylander is more skilled, especially his footspeed which is huge these days.