To start with consider some of these questions;
What type of riding are you doing now?
What type of riding do you intend to do in the future?
What is your budget?
What is your cycling ability?
Some of these questions are easier to answer than others, and some will impact the final decision more so than others.
For example, if you live in a flat area with not a hill in sight, a bike with aerodynamic features or additional comfort is most likely going to be a better investment than a super lightweight climbing bike. If you just need a solid [commuter bike] for work and perhaps some recreational riding on the weekends then you can afford to be thrifty and forgo the bells and whistles. And if you're not a high-level cyclist but very enthusiastic about your riding and have the money to spend, why not go all out and get the bike of your dreams?