I have all 3 on my team
The main things Melo does is score, rebound, and keeps your free throw % pretty high. But if you can get rebounds from waivers, that means it is mostly scoring and free throws that Melo is really helping with.
Drummond+Leonard keeps your blocks high (which is a weak point of yours), keeps steals high with Leonard, and rebounds high (Drummond is likely higher in rebounds than what you can get on waivers by a bit).
I'd say unless FT% and scoring would really help you, I wouldn't go for Melo, because the other categories are likely better under Drummond/Leonard. Although, it would be helpful knowing who is available on your waiver wire that can fill up blocks/steals/assists/rebounds next to Melo if you go that route.