I’ve found mailgun to be very simple and effective. Their dashboard tells you exactly what you need to configure and checks DNS regularly to make sure records stay intact. The rest of their platform is rather simplistic, if you’re looking for more in the way of analytics you may be better paying the premium and sticking with Sendgrid.
Last time I checked MailJet and SendGrid were equally priced, but MailJet didn’t really offer much over cheaper options such as MailGun and ElasticEmail.
I’ve only worked with Elastic Email a couple of times. They do talk about mail reputation on their platform being affected by email volumes below 10,000 messages, so they might be a bad starting point for small communities.
As to ‘best’, it very much depends on your appetite for this kind of stuff. Setting up CNAMEs is par for the course with everyone. All of the companies you’ve mentioned are experts in mail deliverability and that’s part of why they’re recommended rather than running a local SMTP server. If you give us more information on your community size and estimated volumes it would certainly help.