I assume you mean you can only keep one, in which case I’d keep Waller. He is easily among the top 3 at TE. The top tier for QB runs deeper than 3, plus you can stream lower rated QB’s for top tier performance. Gibson is my second choice, although that is based more on potential upside, which isn’t guaranteed.
In summary, Waller can help you dominate a league, but Gibson can only “maybe” help you dominate a league. Go with the sure thing.