>>725758874
Recruiting Waterboy second is more dramatic. He doesn't join during the calm, it's a crisis, and he needs to rise up to the occasion.
Phenomaman's recruitment cutscene is just lame and unfunny.

>>725670419
Waterboy is better mechanically, because you get the opportunity to train him and make him really good. Phenomaman joins at his peak and can't develop any further no matter when you take him, so any missions with him are wasted.
That being said, cutscene for recruiting Waterboy late is much better than the cutscene for recruiting Phenomaman late.