Aren't this one and the same thing? My thinking has always been that a website attracting a lot of traffic will rank better and vice versa. Nonetheless, it makes sense to directly link a lot of traffic to a site that ranks high.The ranking and the amount of traffic it gets are two ways of valuating the worth. Once you get those numbers, then you can find comparable sites in your niche that have recently sold.
I think that if you are looking to sell, what's important is the revenue generated and not just the amount of traffic. On the other hand, I still think that ranking and/or amount of traffic can be a good indicator of how much potential a particular website has.The standard one is revenue by visitors, but if you look at Flippa, one of the main criteria ia how much income the site makes, which is often taken as more important than the site's traffic. There is also a consideration of how long the domain name has been established for, which can affect its ranking and search authority.