I use ActiveCampaign.com. I love it. Easy to use, decent support (although spotty - some CSRs are less knowledgeable than they think).
CRITICAL FEATURE : I can preopopulate Forms. So that lets a user UPDATE their info, it also lets me send them a form prepopulated with their email address so that the form (survey) goes into their record.
This is GREAT for gradually getting more info about your subscribers. (This is a variation of Escalating Commitment)
I’ve tried a lot…
I’ve used CampaignMonitor. Looked closely @ Mailchimp (weak on email automation. was never designed for that), and Drip (a little bit pricey for me (although comparable to the higher featured plan @ ActiveCampaign (I don’t need those features) but it seems GREAT).
Looked very closely @ https://www.agilecrm.com/ but it’s not usa based and support didn’t seem particularly good. (Turns out you want REALLY good support if you’re doing email automation).
Also looked at a number of others (GetResponse)