Like with other vehicles, road bikes feature a large variety of price points and options to meet the needs of different riders. If you're just getting into cycling, you probably don't want to spend thousands of dollars on a bike until you gauge how much you actually get into the sport. Newbie cyclists usually purchase entry-level bikes, but even among these beginner bikes there are many differences. It's important to consider features and intended use when you comparison shop for the best bike for you.
The first consideration to make in choosing a road bike is what type of rider you intend to be. If you're more interested in long endurance rides of 50 miles or more, you'll be better suited to a bike that has a relaxed, upright, touring geometry. On the other hand, if you're more interested in speed, you'll want a bike with a more aggressive, racing geometry. People tend to gravitate to racing-style bikes, thinking that faster is better, but unless you intend to race or do group rides with the pros, keep comfort at the forefront of your purchase decision.
The most popular frame materials among entry-level road bikes are aluminum and carbon. If you have a tight budget, an aluminum bike can provide a lightweight, responsive ride, but you'll experience quite a bit of road vibration. Aluminum frames also have a shorter life than carbon, so only consider this material if you don't intend to keep the frame for many years. Carbon is a more expensive material, but it provides a responsive feel that is much better at dimming road vibration.
The third consideration when comparing entry-level road bikes is the components. There are a variety of groupsets produced by the three main component manufacturers: Sram, Campagnalo and Shimano. If you can afford to get a mid-range groupset, such as one made by Shimano or Sram, this is best. However, if price is a major factor, it's better to spend the money on a good frame than the best components. You can always switch out and upgrade components down the road, but you can't change the geometry or materials of a frame.
The final consideration to make is bike gearing. Road bikes come with double, triple or compact cranksets. A triple offers the widest range in gearing, which is particularly important if you ride in mountainous terrain or are new to cycling. Triples are slightly heavier than doubles, but if you're already strong on the bike or are mostly a flatlander, you can probably get away with a double or compact crankset.