Sleep wasn't nerfed, it actually got better, I meant that ResTalk was nerfed. Because the sleep counter now resets with each switch-in, Milotic may not get the chance to wake up again, and thus would be unable to Rest again to restore its health.
Both have their uses, depends on what you need. Boiling Water may occasionally conflict with Toxic and vice-versa, though, so I'd go with Dragon Tail.