I'm in Southern Australia, with good rain, close to the sea and have volcanic soil which looks as though it will grow pretty much anything. We have two small brewerys within a 20km, and I'll be talking to them about their needs, but wanted a worldwide input too.
If you had ~10 hectares and an interest in beer, which hops would you plant and why?
Cascade. They are the most fruitful of all, easiest to grow, and everybody knows and loves them.
Citra. The new Cascade of the 21st century that most everybody knows and loves. Or alternatively, down under by you, maybe you'd prefer Galaxy which is very similar.
Hallertau. The classic that everybody knows and loves. Not quite as fruitful, but not bad, and you'll never have a problem selling them.
Magnum. High alpha Hallertau. Used for bittering by everyone everywhere.
And that's about it. Those are the essentials IMO. You can make pretty much any beer style with one or more of these versatile hops, never have a problem selling them. They're not just fads. They'll keep you profitable for generations to come, guaranteed.
I like @dmtaylor answer, but here is mine.
Plant as much as possible, the widest variety possible. Perhaps I would plant the most popular in the bigger quantity, but I would still grow other variety in smaller quantity. You should definetively talk to local brew pub owners about not only what they use, but also what they would like to try in the future.
If the local micro brew scene is very active, they will expand and experiment new beers, and that requires not only the most popular hops, but a wide choice. Add some saaz, nugget, fuggle, (east kent) golding to the mix already mentionnend by dmtaylor.
