I'd say that depends on the deck. Also if you want someone to help you making a fusion deck we need to know on what you want to base it? Machines? E-Heroes? Dragons? Spellcasters? or something more particular like Ancient Gear or Cyberdragons? with or without Synchros?
I think there are more important things than the Flute of Summoning Dragon for a Dragon Deck (good side deck card though imo). Lord of D is a whole different story though because he is used to fusion King Dragoon, and King Dragoon is one of the cards with a really good effect. You can use cards as The Dark - Hex Sealed Fusion to substitute Ragnarök or you go for King of the Swmp. Weaker, but he can get you Polymerization out of your deck.