I suppose it would be Wisniewski, at first glance. With his +/- being what it is and thinking it's only a matter of time before Subban gets his shit straight and supplants Wisniewski's TOI.
BUT....as of today Wis has earned a keeper role; EJ has not. Say what you will about EJ but he has actually regressed from last year. Not to mention you already have Pietrangelo - who I prefer over EJ anyhow.
There's no logic behind it, but I'm not a fan of owning 2 players of the same position on the same team. Yes, there are always exceptions, but EJ and Pietrangelo ain't one of 'em.
Honestly, if you're going that route, I'd probably first try trading Wis for a forward while his stock is up.
If that's not doable than ultimately I would probably wind up dumping him over EJ, if only for all the hype/hope EJ has surrounding him. But I certainly wouldn't rule out dumping/trading EJ.