It depends on the decks that you and your opponents are playing. I.e. You're playing as hunter. Hunter suffers from a lack of comeback mechanics so you need board presence or you're screwed. Play the Razormaw on 2 and be happy that you had a two drop. But if you're a Rogue, have a sap in hand, and are playing against a slow deck, then hold on to the Plague Scientist until it can neutralize a big threat.
What your question boils down to is: is board presence more valuable than a battlecry? Each decks reliance on board presence is slightly different. Each matchups reliance on board presence is slightly different. The importance of board presence can even vary within a single game based on what resources you've already exhausted from your opponent, the board state, your hand, etc. Maybe it's not worth it to play a naked Plague Scientist on 3 but it is worth it to play on T8 to combo Vilespine Slayer. There are no hard and fast rules. You just have to learn the matchups, read the opponent/situation, and hope for the best.
It depends on the decks that you and your opponents are playing. I.e. You're playing as hunter. Hunter suffers from a lack of comeback mechanics so you need board presence or you're screwed. Play the Razormaw on 2 and be happy that you had a two drop. But if you're a Rogue, have a sap in hand, and are playing against a slow deck, then hold on to the Plague Scientist until it can neutralize a big threat.
What your question boils down to is: is board presence more valuable than a battlecry? Each decks reliance on board presence is slightly different. Each matchups reliance on board presence is slightly different. The importance of board presence can even vary within a single game based on what resources you've already exhausted from your opponent, the board state, your hand, etc. Maybe it's not worth it to play a naked Plague Scientist on 3 but it is worth it to play on T8 to combo Vilespine Slayer. There are no hard and fast rules. You just have to learn the matchups, read the opponent/situation, and hope for the best.