If I had to choose, Gardiner. He skates well and usually does a decent job evading forechecking pressure, but he's so weak and has nothing but rocks in his head. He relies purely on his ability to out-skate opponents, so when it works it looks awfully nice, but when he's not doing that, he's constantly flubbing on easy passes, throwing the puck to teammates who aren't open, getting caught too far up the ice for even when there's absolutely no conceivable reason not to be staying back, etc. etc.
Franson has had a bad season so far, but at least he's proven capable of putting up pretty significant offensive numbers in the right role, while also looking decent defensively (not this season, but when playing more sheltered minutes with Fraser), and having an excellent point shot and a good outlet pass most of the time. He can also throw a helluva hit too, when he wants to.
Don't get me wrong, I like Gardiner's upside, but holy lord god has he been frustrating to watch ever since coming back from that head injury. One shift he's cutting through the other team's neutral zone trap like a knife through butter, the next shift he can't complete a ****ing three foot pass and roves around like an idiot with little to no regard for where anyone else on the ice is.