Companies for Seminars and Webinars?

I am primarily seminar based for my marketing. I am curious to hear who everyone is using for their seminars or webinars, or are you just designing the mailers yourself and using a third party for the lists like Salesgenie? I'd be particularly interested in those who are doing digital marketing rather than postal mail to either get people to a physical event or enrolled in a webinar. Please share your experiences on ROI for webinar vs seminar as well. I'd like to "modernize" my process to include either digital enrollment and/or delivery and appreciate anyone's experiences.