We must try to think about what is best for him; ....., we must consider what he himself wants to do.

Equally introduces a balancing consideration - it suggests giving the same weight to both factors mentioned: what's best for him AND what he wants. The sentence structure requires a word that connects these two considerations. Exclusively would mean only considering one, effectively would mean successfully, exhaustively would mean thoroughly, and evidently would mean obviously. Equally is the only word that creates the required balance.