Just a few thoughts.
I've been involved with many different transactions involving licensing and the sale of IP rights. Based on these experiences, most of my clients base their answer to the question of sell or license, in large part, on how involved do they want to be after the transaction is complete.
A sale involving a single payout is great, in that once it is over, its over. But, the downside is if the business "takes off" you don't get the financial benefit.
If however, you establish a license between you and the other party, you may see higher dollars if it grows, (less if not) but you will always be attached to them for the lift of the agreement irrespective of how the business is going. As a licensee, you have obligations regarding monitoring their use of the mark. If you do not monitor or otherwise exercise control over the mark, you may forfeit your rights.
Some clients are ready to sell as they do not want anything else to do with the business. Some clients do not want to be invovled as they will have a tendency to want to be a part of the business but cannot do so. Still, others don't mind have another person running the business.
If you sell, you can always seek to have a buy-back provision in the event of certain events, such as bankruptcy or the closing of the website. You can also see to have installment payments based on performance over a period of time. With a sale, there are always various ways to make a deal. Just remember, for everything you want, they will also want something in return, i.e typically a reduction in price.
I don't know know if this is the type of information you were looking for. I hope it helps in any event.