The place to start is with a good bike store. Look in the phone book for bike stores in your neighborhood. Visit two or three stores. You are not just looking for a bike. You are looking for a relationship. The RIGHT store will have:
-someone willing to answer your questions and show you bikes in your price range
-someone on-duty to make adjustments to the bike that you buy (at smaller shops, one person might be the person showing you the bike, and setting it up for you).
In a given price range, there is not a big difference between brands. Each brand will have a metal frame, supported by two tires, holding the selection of Shimano parts that is standard for that price range. So, your satisfaction from a $400 bike depends on getting a bike that fits your height and weight, and is tuned up and adjusted to ride comfortably and safely.
Unlike a sporting goods store, or discount store, a good bike shop expects you to bring your new bike back in a few weeks. The cables on a new bike stretch, and bolts sometimes needed tightening. Wheels sometimes need a bit of re-truing after a few weeks of riding.
Based on the description of your riding plans, a good bike to look at would be the Trek 7300FX. With light, slick tires, it is a good road bike/commuting bike. With heavier tires, it can be used on smoother dirt trails. It comes in five sizes, so almost any rider can get a good fit. After you "test ride" a Trek 7300FX, try some $400 bikes from other companies to see how they compare. That is a "price point" where most companies offer several good choices.