Originally Posted by thommy

no matter what you have you should always try to redirect to ONE version.
a site with and without www. existing is DC but google can handle it as long as there are no missmatching in the rest of the site. but i would always recommend to redirect to one version.

as saretta perfectly explained the 301 (moved permanently) will catch all linkpower and lead it to the final end. the same is with http and https. no matter if all your linbks are going to the http version through the redirect google will know that this http site is PERMANTENTLY moved to https.