The problem with MailChimp is that it's very simple and easy to use, and once your list actually gets popular the pricing falls off a cliff. At 2,000 subscribers MailChimp is free; at 3,000 it's $50 a month, and it keeps going up.
There's no monthly fee to send email through Mailgun, and the only thing they charge for is number of emails: you can send 10,000 a month for free, and it's $5 per 10,000 after that. You can also manage mailing lists directly through mailgun, but it doesn't have as polished an interface (and you need to send the actual mailings yourself through the API). So if you want a polished interface, use MailTrain to manage your lists and Mailgun to send the emails.
Amazon SES is even cheaper, and also hooks into Mailtrain. "$0 for the first 62,000 emails sent per month, and $0.10 per 1,000 emails sent thereafter."
MailChimp offers better deliverability than Mailgun and SES, but at a pretty steep cost. If you're a professional company with income, pay the $50+ a month for Mailchimp. If you're doing a list for a sidegig or a hobby, use Mailtrain.