Generally, prosper tracking202 is better because you can dynamically track keywords if traffic provider (like Adwords) will give you macro which you can include in your link.
So,
your url can look like that: tracking202.com/go.php?keyword={!keyword!}
and if somebody will click on ad on keyword 'lol cats' he will be sent to tracking202.com/go.php?keyword=lol cats
if this user will buy something on your sales page, then you will know that keyword lol cats is profitable. tracking202 got build-in tracking system with pixel/postback announce of sale.