If it's the horrible "Borg-are-everywhere" universe described here, I've gotta go with Worf. He's got the most experience dealing with Borg, and possibly the most combat experience overall. Tuvok would be my second choice.
I did briefly consider Landry, since she also has wartime experience. But she also [spoilers redacted] in two universes, which makes me think she probably wouldn't actually be that handy to have around. I was going to say something about leaving Ash Tyler off the list of choices, but... yeah.