The only thing that keeps me from voting 'Hero' is the way she helped the Borg in Scorpion. She hung entire worlds out to dry there.
You think the 8472 wouldn't have slaughtered those people?
Uh, the only thing 8472 is guilty of is maybe using excessive force in defending themselves. Maybe. They had every right to tear the Borg a new one for attacking them. They had every right to assume Voyager was an enemy when they boarded their ship, tried tractoring it, and beaming it away in their first encounter and then were seen collaborating with their enemy from that point on. Then invading their realm and using biological weapons didn't help either.
And before you throw out that "the weak shall perish" or "your galaxy will be purged" just remember... front line soldiers say crap like that all the time. Not to mention we have only Kes' admittedly sketchy telepathy to go on with that. If an American solider says "Kill em all!" that doesn't mean we're a nation of genocidal manics bent on exterminating all other nations. When an important 8472 showed up later on they were quite reasonable actually.
So yes... Janeway basically aided the Borg in fighting an enemy just to get what she wanted. And they betrayed her, surprise, surprise. I'd be pissed off at her too if I was Arturis.