Been using AWS SES, dirt cheap and works like a charm.

I use web3forms in my website, it's free and easy to use.

Recommended it before in other threads, I'm a big fan of CloudMailin [0] -- they've got some great inbound and outbound services, generous free tier, very simple integrations, useful and reliable dashboard. I've used SES, SendGrid, MailGun, Hive, Klaviyo, etc, but at the end of the day had an overall easier, better, more enjoyable experience with the bare simplicity of CloudMailin.

[0] https://www.cloudmailin.com/outbound

Brevo.

mostly used aws ses and resend

learn how to read a manual and use sendmail.

you only need dns and spf txt entries. unless you're a spammer.

None. Just use SMTP. Any email provider can handle thousands of emails without issues. Only if you need to send 60k newsletters at once are these emailing services useful.