What good single opt in autoresponders are there out there??? (HELP!!)

Use the basic HTML tool that the ESP offers to create a form with the necessary fields.

Then hire someone from a freelancer site (I like upwork) to make it look how you want it / responsive and host it yourself.

TL;DR Try Mautic

I just finished switching over from Mailchimp to a self-hosted Mautic install and as far as I can tell you can do pretty much anything with it. I'm not a particularly techie guy so I followed a few youtube videos to sign up for and setup an Amazon EC2 instance (aka VPS), which is free for a year by the way. And they have a free one-click Mautic install from a company called Bitnami.

If you don't want to go with Amazon you can also do a Softaculous one-click Mautic install on any cpanel host.

Since I signed up with Amazon for EC2 I went with their SES service for sending emails too. Set both up in the same region and man it's smooth as butter! Takes about 1 second to deliver an email to any of the major hosts (gmail, hotmail, yahoo etc.) and I've had zero issue with inboxing.

Now my lists are tiny so I don't have any personal experience with how much the free tier EC2 can handle, but I've heard some people have had no server slowdown with up to 15,000 contacts.

Anyway, back to your original question. If you don't like the built-in forms and landing pages with Mailchimp you're going to hate the ones Mautic comes with, because frankly, they look like ass. However, everything is 100% customizable. You can modify the forms any way you want with your own CSS and host them on any web page, and there are videos on youtube walking you through that too. If you're using Wordpress there are also several form plugins that integrate with Mautic. I haven't tried any though so I can't give any recommendations.

Mautic is also single opt-in by default. You would have to deliberately build confirmation into a campaign if you wanted to create a double opt-in list.

The cool thing about Mautic is that it's so much more than what any ESP offers. It handles forms, landing pages, email, SMS, social media, and asset delivery (think pdf's, audio, video etc.) to manage complex funnels and drip campaigns to an unlimited number of contacts, and you only pay for the messages you send.

Amazon charges $0.0001 per email. Twilio (the default SMS) I think charges $0.0075 per text. The only other cost is hosting for your VPS. Like I said Amazon EC2 t2.micro (1gb RAM, 1vCPU, 30gb storage) is free for a year and then $9.50/month. You can get a comparable VPS from places like Digital Ocean and Linode for $5/month, or even cheaper from one of the hosts at lowendbox.

One caveat. Since it's a multi-faceted self-hosted open source solution, Mautic definitely requires more tinkering than a simple ESP. I've had relatively few and minor issues and have been able to solve them with google and youtube. But if things went really bad I would definitely need to hire a freelancer to sort it out.

I am using Aweber and GetResponse, both support single opt-in. In terms of nice looking forms, I think GetResponse have better design.

I have used Aweber and it works wonder. Try it!