Forms are common within all the top marketing automation solutions. Each allows you to build, customize and reorder fields within forms, save forms, assign them to categories, and to view results.
Drag and drop editors are common in each, with the easiest and most robust form creators located within HubSpot and SharpSpring.
A key feature to look for are dynamic forms that allow "auto-complete" based on stored information or that allow you to offer different questions to repeat visitors. For example, if someone has visited your website before, and you already know their first name, last name, company, e-mail, and phone number - why would you ask for that information again? Or make a person resubmit it? By using dynamic forms, you can ask repeat visitors different questions and gather more information for your marketing and sales efforts.
Another important feature to consider is whether or not you can integrate your own website CSS into the form design, and whether or not you can use forms native to your website or a third-party's form. Some of the automation solutions referenced here, SharpSpring is one, have built-in integrations with form builders such as: FormStack, Gravity Forms, Wufoo, Sugar and Salesforce.
Lastly, you may want to ask if your automation solution can integrate its forms with Webinar providers, such as GoToWebinar. In some cases, but not all, these integrations are built-in, but you need to ask to confirm.