Lemieux.
Orr continuing post-injury is like Gretzky after the "trade". Can he keep it up longer? Can he maybe do "a bit better" than what he's already done even? Certainly some exciting stuff, but for the most part, you already got to see full seasons of Orr at his best, and it was grandiose.
Lemieux is like Gretzky if after his season of 212 points/92 goals in 1982, instead of spending the next 4-6 seasons also averaging ~200+ points a season, he got injured in every year, had cancer, had debilitating back problems so that even when he *did* play - he wasn't exactly at his best. Skip a few years - and you get post 91-92 Gretzky (or Lemieux) playing a few seasons again.
Basically - we never really got to see Lemieux at his best. He clearly hit another "gear" starting around 1988 and 1989. 1989 was a great season. Than injuries, health. He got the 2 smythes (amazing performances) but he wasn't 100%. Even 1992-1993, his historic season, he only played 60 games and everyone knows what was going on.
To be clear - I'm not saying Lemieux would have beaten all/any of Gretzky records in those years (~1989-1995) had he been healthy - I just would have loved to see him attempt to, to see what he could have accomplished.
Orr - we pretty much already saw full healthy seasons of his in his prime/peak. I know he had knee issues, but i don't think those affected his best seasons as much as Lemieux was impacted with his issues.
I do think that - full healthy & long career, Orr has much better chances than Lemieux to top Gretzky all time. Defensemen typically age better. But it's the "peak" that excites me, and we saw peak Orr, we barely saw peak Lemieux.