If you are a solo salesperson or sending low volumes, and know what you're doing, we recommend starting with Pro. This is priced comparably to services like Lemlist or Apollo but is far easier to use.
If you are already sending significant volumes of cold emails or want to send significant volume, then Growth or Scale are the best choice. Significant volume means over 500 emails per month. At that volume you need multiple emails and you begin to risk your domain reputation, so you also need at least one secondary domain.
If you are choosing between Growth and Scale, we recommend starting with Growth unless you know you need to do the volumes of Scale. The setup and work required by you is the same–almost none!–but Scale is significant volume, so you'd only want to do that if you know that email is working for you or if you have a lot of different ideas to test.