People are really overrating the Rift thing. Yes the Inquisitor can open a rift inside someone but you think the Warden or Hawke are just gonna stand there while the Inquisitor opens a Rift inside them? No way, they'd move and attack. To open the Rift, the Inquisitor has to power up, can't just flick your wrist and do it. To get ride of the Warden or Hawke that way, the Inquisitor would first need to beat them down so they can't fight back and in a 1-on-1 fight? I'd put my money on the Warden.
So, 1-on-1 to the death?
Hawke vs. Inquisitor? Keeping in mind that the Inquisitor would have to beat Hawke down long enough to power up to open a rift, I'd say its a tie, but leaning towards the Inquisitor, specially mages since I think KE beats Force/BM, Force/SH, or BM/SH.
Hawke vs. Warden? I think the Warden would crush Hawke. People argue that the Warden's only good for darkspawn, but if anything darkspawn should be harder to kill than your average bandit or thug since they're not human. Mage wise, AW/Anything crushes anything Hawke could do, without even taking into account a third specialization
Warden vs. Inquisitor? I think the Warden would win that one too. The Inquisitor's great, but I just think the Warden is more powerful. Mage wise, AW again owns, though KE is better than Force mage for Hawke.
Warden vs Hawke vs Inquisitor in a threeway battle would probably be to chaotic to decide, if all three are mages, probably the Warden, cause Mana Clash plus AW beats the others, but outside of the game mechanic, I could see this being a tie. Three badass fighting each other is recipe for disaster since I can't see anyone dominating too much when they're out for themselves.
On another note, you Origin companions vs. DA2 vs. Inquisition? Varric counts for Hawke since they have less companions, I'd say Alistair, Leliana, & Morrigan would beat Aveline, Isabela, & Merrill, but Cassandra, Cole, and Vivenne would beat them both I think.
Morrigan was great but KE destroys Shapeshifter, though if she's an AW I could see that go either way. Cole's great he'd have to get to Leliana so distance swing that in Leliana's favor but if they start in front of each other, Cole could kill her quickly. Cassandra would beat Alistair, I think by quite a bit.