The answer depends on the product and the revenue model as a whole. Boxed sales will create an initial cash injection and normally loyal players who are willing to spend time getting to know the product, as well as a small percentage of impluse purchases.

Digitial downloads can offer a quick fix for people who are interested and require an (almost) instant way to get the product and provides a great margin.

Free download increases the product audience but does not mean people have any loyality. There are also implications in terms of bandwidth and support when you offer free downloads which need to be considered and managed.  

Is the game F2P or P2P? Should the game have advertising? Which payment options and plans should you have? Do you really need game time cards in the stores? Are micro-payment viable or needed? Mobile phone support? What other revenue generating opportunities are there?

What are the cash flow implications? When's the breakeven point? What's the minimum users you need to have to pay the bills?