I've been using the Mailchimp plugin but I do miss some advanced features.
For example, setting a placeholder text for input fields so I can create a more compact signup box without labels.
And the ability to activate a honeypot field and to completely remove the firstname and lastname fields from the code. Now I do get signups with strange names, probably because there are a bot.
Although I customised the plugin to my needs but these changes get lost on a update.