You will not find very many people who will voluntarily add a banner ad to their site, unless there is a commission or some compensation involved. It is much easier for people to add a text link if they like your site.
As far as
SEO goes, make sure to use a direct hyperlink and place your keywords in an ALT attribute. A simple text link with keywords in the hyperlink is best, but if you are going to use an image, use the ALT attribute for the keywords. Using keywords that describe your offering is better than using the company or web site name.
Use an actual URL for the hyperlink. Do not add a code or attribute to the URL to identify the source. With direct hyperlinks that creates duplicate content URLs. You want one and only one URL to represent each page in your site.