You can't go wrong with Trek and Raleigh, both are good bikes. Not familiar with Sun's bikes.

If I were you I'd test drive all of them and see how they feel. The LBS should be able to help you decide which one fits most properly. Thats whats most important, more than the specific brand you choose.

The Trek 7100 or the Trek Navagator 50 looks like they would fit your bill. I'd go with the 7100 because it has 700 sized wheels, which work well on most surfaces. You couuld look at Treks "Cruisers" which are also in your price range. I'm not sure why anyone would want a cruiser as a primary bike, they're somewhat inefficient. You can compare the components offered on each bike. With a $250-300 bike, you're looking at entry level components. good luck