Lion is the stronger training choice for the example card configurations below. Both pets are Rare.
Lion provides 8,800 more Power per training hit, approximately 74.6% more than Crocodile in this comparison: (20,600 − 11,800) ÷ 11,800 × 100. This is a comparison of those two configurations, not a fixed species advantage; use your current cards when deciding which pet to train with.
Both specials have a 12-second interval and include stun. Lion's King's Roar adds knockback, while Crocodile's Swamp Whirlpool adds slow. Favor Lion when pushing enemies away is useful; favor Crocodile when slowing their movement better fits your positioning.