I chose Postmark over Sendgrid because Postmark supports bounce callbacks for any volume, but for the same feature from Sendgrid we would have to pay $80/month, and we didn't need to send even a small fraction of the emails that that plan includes. You should compare prices based on your expected volume, not on some hypothetical maximum.

Something else to keep in mind is that some of these services reviewed are explicitly not intended to be used for bulk mail marketing campaigns but only for individual user targeted emails such as order confirmations.