Willpower is useful with any fight that will inflict non-damaging debuffs. A fight against a Science Doombot can get you back up to full within seconds and is extremely useful in recovering health without using potions.
Willpower is more generically useful (as long as you aren't fighting Warlock), but if you play a lot with champs who rely on regeneration, then Recovery starts to be really useful.
Obvious candidates would be Wolverine, X-23, Ghost Rider, but also Ghulk, G2099. With Recovery, you can tank hits with Magik during Limbo to use it to regenerate.
Given that willpower is expensive and requires a ton of points in defense to keep open, recovery is better. They should have dropped the cost and requirements when they nerfed it.
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Obvious candidates would be Wolverine, X-23, Ghost Rider, but also Ghulk, G2099. With Recovery, you can tank hits with Magik during Limbo to use it to regenerate.
Use both. Are they super expensive? Yes. So grind them over time. Nothing is more useful to spend your units than on the right mastery.
And they are both worth it 100%