Tough one.... Not a bad problem to have though. I would say keep Gronk. Whitten does catch more passes and in a PPR league can really explode if he tacks on a TD or 2. However, I think Gronk is more consistent strong scorer and you will need that in playoffs. Plus, consider the QB.... Who woul you rather have throwing to your TE? Don't think you can lose either way you go though and should be able to cash in pretty well on either.