So, for a second, imagine yourself as Morrowseer. Your prophecy is important to your tribe, but both sets of dragonets you have are horrible for your plans. Who would you pick? The Skywing can't be swapped out of course, so you're left with other choices. What would you pick?
Skywing: Flame
Seawing: Squid or Tsunami
Sandwing: Sunny or Viper
Mudwing: Ochre or Clay
Nightwing: Starflight or Fatespeaker
My list:
Skywing: Flame - Obviously
Seawing: Squid - Tsunami is too reckless and rebellious, and Squid could be controlled through treasure
Sandwing: Viper - Sunny is 'defective' and not good for most combat
Mudwing: Clay - You would think Clay would have more abilities than Ochre, and is much more strong and less lazy.
Nightwing: Starflight - Starflight has already angered Blister, but Fatespeaker would make others question Nightwing powers, and is less smart and more annoying than Starflight.