Everything is on the link I pasted.
Things to consider if you choose Sparkpost:
- Email will appear as send by sparkpost. You cannot whitelabel completely this. (you can with mailgun and sendgrid).
- You will need to disable the unsubscribe on the API. Make sure you do this on each email. If you use SMTP (as I do on my website) you cannot disable it.
- No test mode. Mailgun has it.
The rest looks fine and the 100k is a nice thing to have, for me I will use Mailgun and Sendgrid, but I can understand that this could be good for others.