I wasn't sure what to think when I clicked on the thread but it seems most of this board is of the same mind as me.
The first name that popped into my head when I saw the question was Morgan Rielly, but upon second thought, the answer is Cody Franson.
That's saying something because if you asked the worst defenseman last year, he'd be the overwhelming choice. Quite an improvement, although apparently last year he was dealing with some lower body injuries which hindered his mobility.
Would I pay him what he's going to ask in the summer? No, because it's Franson, and you know he's going to be asked to be paid like a #1 despite the fact that he's a #4. But a #4 who puts up the points that he does is nonetheless a very valuable piece who should command a nice return at the deadline if we go that route.
The other factor, as well, which isn't often mentioned: The guy seems to care. For all the heartless performances we've seen this year, even when he was terrible last year, he's never hidden from the cameras. He's always been there to answer for his and his team's play and the answers that he gives are not the usual cliches. And let's not forget the whole salute fiasco, where Franson was only guy skating towards center ice. Lots of players say they want to stay in Toronto. Franson grew up a Leafs fan and I believe he truly does. Sadly, his agent is one of the worst in the business.