I don't know anything about Paul Martin, so I can't tell you who I'd prefer.
What I can tell you is that Backman has come out of nowhere this year and has finally began to develop into the player that everyone expected.
That said, it's hard to predict how much value he'll provide to your team this year. Just a quick look at tonight's box score shows he played about 16 and a half minutes and his ~4 minutes were only topped by Pronger on D. He'll probably be on the 2nd pairing for the rest of the season, unfortunately he's been paired with Khavanov, so his plus-minus will take a hit.
This season, the most I'd see him ending up with is 25-30 points. I'd keep an eye on his PP minutes over the next couple weeks if you're interested in picking him up.
Career-wise... he'll probably top off as a 3 or 4 that gets good PP time.