I'm not keeping the Rangers 1st because of a 1% chance it ends up McKenna, which I think is a pretty accurate estimation for how likely that pick is to become McKenna. That said, the 1st looks pretty likely to be at minimum in the 10-20 range and you can obviously get core players with that kind of pick. I'd trade it if you can get an equivalent upside player that's in the NHL already, like the Dougie Hamilton example that I already mentioned, but I'd be extremely picky with that pick if I'm trading it.
Either a C with fringe 1C/2C upside or a top-4 D with #2/3D upside is the only thing I'd trade it for. The only player I see in the RFA market this year that I may pull that trigger on is Rossi. McTavish (isn't good enough yet), Byram (isn't good enough yet) and Peterka (doesn't play the position I want) are also close that I could probably be convinced of, but Rossi is the only one that fully hits it.