I can make an excellant argument that, if a person is only going to have one motorcycle, that a dual-sport is the bike to have.But you must always remember that this type of bike is the biggest compromise machine out there, meaning it will never be the best at anything other than being a great dual-sport.But a good dual-sport thumper(mines a 1982 Suzuki SP500) will give the sports bikes some real competition in really tight,winding roads.They don't have the horsepower, but they are narrow, and really flickable in the twisties.They also can get great gas mileage(mine averages 65 mpg, and can cruise at 55-65 mph).They are light in weight, compared to pure street bakes, and the newer ones stop really well with a single disc at front and rear.Try taking a Ninja down a fireroad, or dirt trail.
I understand the new Suzuki DR400 is a great machine. The Kawasaki KR650 is a bulletproof bike with a huge gas tank(about 6 gallons).Suzuki's DR650 is also a fantastic D-S bike.Honda's big XR650L is a great one too.I like my older Suzuki because I can touch both feet down flat-footed at the same time-the newer ones are way up there.
Having said all that, my other bike is a 1990 Kawasaki EX500(pre-Ninja). I feel like I have a couple of great bikes in both catagories.
I just thought I'd support the Dual-Sport concept. as in this crowd, it's likely to be a little biased.