Right now Drouin is way ahead. He is an established impact NHLer, and currently #13 in points for a LW, so top line #s.
Sergachev's situation is a bit more complicated. It's debatable he should even be in the NHL at this point, getting very low minutes. But he does contribute on the score sheet and I guess management prefers he get NHL competition even if it's limited over bigger minutes and role in the minors. I would say he is basically still a prospect, and he certainly has a long way to go before you pencil him in as a top 4 D let alone top pairing and it's possible he never figures out the defensive aspect well enough to be more than a PP specialist, which is still something but not quite as much as a lot of people would hope.
So given all that, Drouin has a lot more value than Sergachev but people have to remember this was never an even value trade, it only happened because of the expansion draft. Bergevin was one of the few GMs in a position to take on a new protected contract before the draft, and willing to deal futures. Yzerman needed to unload a contract so it wasn't really Drouin for Sergachev straight up, it was Drouin for Segachev + Killorn (who he was now able to protect after the trade)