Do both, but...
It's known that readers don't do blogs anymore, either. Unless you're producing interesting content (not just about your books, writing, etc), then you won't get a lot of readers on the blog. It's best to just use Wordpress.com as a website instead to list all your books, then a mailing list like Mailchimp to attract readers.
I'm sure you've browsed to a website or blog and noticed the popup that's right in your face as soon as the page loads. That's the mailing list form. They both work together.
Alternatively, you can start with a free website maker like Weebly or Wix and use Mailchimp with it. When you have the money, upgrade to a paid site. Also, remember most emails now-a-days filter advertisement emails as spam. So if you're sending Mailchimp updates via Hotmail or Gmail, these can get vetted by the reader's email and they might not see them. It's really a good idea to spend a little extra to get a professional email address such as:
[email protected] .... of course, that is if you're planning on building a mailing list.