I'd take MDZ.
MDZ has surpassed Whitney as a player at this point in a head-to-head comparison, and seeing that your league also includes playoffs, I generally like the Rangers chances at making the playoffs in the East over the Oilers' chances to do so in the West (and that despite the fact that the Rangers are currently 3 points out and playing like hell compared to the Oilers being 2 points out, and also notwithstanding that the Rangers having one less game remaining than the Oilers do). With Whitney, you just never know. Will he get hurt again and miss time? Will he go back to being a healthy scratch again for some/stretches of games? Just too much uncertainty there for me.
Where this could become slightly complicated is if the Oilers are able to deal Whitney to a contender at the trade deadline ... that certainly could impact the analysis given that playoffs count. But that possibility involves too much speculation from my perspective, both in terms of whether (a) that will even happen (it's been reported that the Oilers have been shopping him forever and receiving little interest); and (b) what Whitney's role would be on that new, and presumably, better team.