As Fury you need both, Deathmaker is a single target legendary and falls behind whenever Bladestorm has value. If you look at Warcraft logs the fights with AOE burst favour Signet, the fights with single target favour Deathmaker, the fights with both are split.
Sire Heroic top 10 parses has 5 signet users and 5 deathmaker, but with M+ added into the situation it’s a clear win for Signet. So if you have to make one, make Signet, because you can also use that for Arms and Prot.
It was recently discovered that Signet wasn’t entirely optimized for Fury in the APL for the Simulations. Signet is the best choice for Fury in every scenario, and the sims should soon be updated to reflect this.
Signet forces you to play bladestorm and anger management, but as people above mentioned its numerically the best, its useful in both raids and m+, its useful in both aoe and st, and its usable by both other warrior specs too.
Unless you absolutely love deathmaker for some odd reason and enjoy the game more with it, the logical and optimal choice is to go signet.