You want single coil or multi coil. Lung or mouth draw?
For me, with a 20w device, I'd go for a Kayfun or the like, maybe a subtank or the like. Maybe an Orchid if I decide to do dual coils. The Nautilus is a nice Clearomizer, for a spinner or Ego battery. People do use them at 15watt or more. BUT they were designed for less than 10watt devices.. Why not get the type of topper your device was intended to run.