I don't know about effects on ranking. If the listing is under your profile, then you will be the host, and you can make the owner a co-host. If the listing is under the owner's profile, the owner will be the host and can make you a co-host. Co-hosts can't do everything a host can do; e.g. they cannot ask for or send money via the resolution center, and can't see all review feedback. So if the owner is not planning to actively participate in hosting, it would be more convenient for both of you if you are the host.