so I've been a long-term user of Omnisend as an email marketing platform now and I can without no doubt say that I will be using it in the future. I've tried Mailchimp some time ago, but due to shortage of features I, as an ecom merchant, changed to Omnisend. For example I need "hooks" for my email pop-ups and newsletter, which Omnisend provides (like Wheel Of Fortune for example). Some campaigns need more love, therefore I can use a feature called Campaign Booster which Mailchimp does not have. Also advanced and more ecom oriented automation workflows. And last but not least - SUPPORT. Okay, support-wise Omnisend is fantastic hands down, 24/7 reach.
Cons - well they do not have any Advert platform intergation yet, but they promise to have them done by summer.
So these are my two cents lets say.