I always feel like McAvoy is older than he is for some reason. Like my initial reaction was, "Heiskanen-McAvoy is easily the best duo right now" but thinking 10 years is a long time, so McAvoy's age works against them. But then i remember that he's actually still really young. So i go with that.
I think it's McAvoy's poise and complete all-around game that just feels more mature than his age. He's also been playing at that high level for a while now, while some others are still just emerging.
Hughes kinda kills that Makar pairing for me. They'd be a terrible fit together, and i honestly don't know how much room you have for building around Hughes unless you have a true matchup/shutdown stud on the other pairing to work with. Which Makar isn't quite.
Seider-Fox, i hate the premise of as a pairing playing together as two RHD. So i disqualified in on that. Anchoring separate pairings, i think it offers the sort of diversified 1-2 punch that Hughes-Makar is lacking. But i'm not as high on Fox as a lot of people, so they fall short for me.
I did consider Dahlin-Dobson...but they're certainly the least "proven" pairing here. It's worth thinking about, because the upside with both is sky high, and their age is a beneficial factor over the course of a decade. But it's a little bit too "risky" in the context of a pairing like Heiskanen-McAvoy being an alternative option, and really not enough of an age difference to worry me over most of the ten year term.