I find sending postcards to someone who is in your mailing lists incredibly creepy.
To send a postcard to someone who was in our mailing list and opted out is incredible creepy times a thousand.
Mailchimp allows its clients to do just that. And yeah, it's creepy, even if you don't use the service.
Anyway, I've had Mailerlite for over a year, and I never had any problems other than an automation that it didn't execute. I wasn't happy about it, but would have continued using the service if it wasn't for the growing price.
One thing I noticed is that if you use newsletter magnets and participate in promos your list can grow incredibly fast. I scrubbed, scrubbed, scrubbed and I have 2k now, but if I hadn't been scrubbing I could have some 4k.
For this reason I decided to change to a newsletter service that allows me to grow. I want to have a new newsletter magnet in a few months. I felt that I was trying to keep my list under 2500 to decrease the plan, and wanting the newsletter not to grow is not a good mindset.
I got Sendy. It's complicated but I had someone set it up for me. It doesn't have pretty templates, I'll have to import them from somewhere else, and its sign-up forms are hideous. I got a plugin for pretty forms. I'll start using it in July (my current ML plan is until August) and I'll report.
So yeah, there are other alternatives. I also looked at MailOctopus and MailJet, which have positive reviews and aren't expensive for large lists either.
So people who are jumping out of Mailchimp could also look at other alternatives and consider the fact that the list is likely to grow.