For social media posts, is it better to post the Constant Contact generated URL or your website URL?

In social media posts, is it better to post the link to your website that advertises a specific event, or the URL to your Constant Contact (or other mass mail program) e-blast that advertises said event?

The details: our company often sends e-blasts out via Constant Contact to advertise training conferences that we produce, with the ultimate goal of increasing registration/attendance. These e-blasts are well-designed and often contain multiple elements pertaining to the conference: a section and link for optional training courses and a section and separate link for actually registering, for example. All of these same links are housed within our actual website, under the umbrella conference page. So is it better to post the URL that CC generates for this eblast to Facebook and other social media platforms? Or is it better to customize a different type of post (one more truncated in content than the e-blast and more geared for social media) that uses some of the text and images from the CC eblast and includes a link to the actual conference website "for more information and to register"?

I was always under the impression that the ultimate goal was to direct traffic to your website, rather than sending your followers elsewhere (in this case, Constant Contact's website). If the social media user clicks on the Constant Contact URL, they will still need to click off that site (back to our site) to register (or learn more about the training courses, etc) so for the purposes of social media posting, I thought I should just cut out the middle man altogether and send them directly to our conference website which, in theory, if it's designed right, should offer them access to all the information they need and want. But perhaps that is not the best strategy? A small side note: I was informed by Constant Contact that they don't tract link clicks to this URL they generate, so there's also no way to track the clicks using this URL, whereas at least we can track traffic to our own website from social media.

I know things change rapidly in social media and I want to stay current with the trends, so I thought I'd better query the experts on this. Thanks so much for taking the time to read and respond to this!