Gudbranson is -5, and having a terrible year as well. Kulikov is -9 but had harder matchups, according to the Panthers forums. Also, Panthers fans are afraid to trade kulikov they say he's much better than his stats are.
That's what happens when bad teams give #1 D assignments to #2-3-4 D, their stats suffer.
It's fair to say that Markov would be #1 on a lot of teams, he's clearly superior to Kulikov right now, but Kulikov has high upside too, he's still raw and young. IMO he's worth a substantial offer.