Banner Buys - How to track offers, links, landing pages?

Let's say you have a site to advertise your banners to. You have your offer (cpa / clickbank). How do you go about tracking?

Do you

a) Direct link from the site using a banner to your cpa / clickbank offer? or...
b) Link the banner to your landing page first for optin then to cpa / clickbank offer?

How do you track the effectiveness of the landing page from a given site? How would you go about tracking if people from the site respond better when directly linked to the offer or first to your landing page for optin and sell on them later on?

Now what if you have multiple different sites to advertise your banners to? How do you know which approach is best for each site? Do you track each approach (a or b link) with each site? Simultaneously? (per page load) Do you create different links (a or b) for each site? So some sites show people respond better to an optin while others are on the buy mode and respond well when linked directly to the cpa / clickbank offer?

or are these all done by a tracking system / solution? What providers are out there?


Please help a newbie out.