I'll cut straight to the fact. When choosing what wording to put at the bottom of your subscriber emails, choose "Unsubscribe" or "Unsubscribe Now". DO NOT use only the phrase "Manage Subscription". This is a shady practice and not cool from a UX perspective. More than likely the person is pissed off that they somehow landed on your subscription list and they just want to be removed NOW.
Psychologically, when I see "Manage Subscription", I'm thinking something along these lines: "Oh this shitty company doesn't want to make it so easy to get me removed from their spam list, screw them, now I'm really pissed off". Is that the feeling you really want generated towards your company?
On the flipside, if I had a company, and I was sending emails to subscribers, I would want to make it extremely easy for people to unsub because I wouldn't want to create that negative feeling towards my company. I would want to get the unwanting people removed as quickly and easily as possible.
At a lower level of thinking:
If your company isn't doing something that creates real interest in a regular email to subscribers, then you're doing something wrong, and you should not be penalizing the people that want out of your boring crappy spam campaign.
However: If you truly do have options that the person CAN "manage".. then use both links. One to appease the likely case as described above(the quick unsub), and one for your real subscriber that truly wants to edit the subscription settings.
In summary.. Do to others what you would like to have done to you. ie: Don't be a dick.