The most important factors are: Make sure it fits you, make sure you like your seat, make sure the bike is suited for the application that you want to use it and price. All these factors can be easy to find if you go to a good bike shop. Good luck!
Go to a bike shop and they can answer all you questions. They will fit a bike to you and make sure that it is operating properly. You first need to determine what you want to use the bike for and where you are going to be riding. Google bike shops in your area.
The most important factors are: Make sure it fits you, make sure you like your seat, make sure the bike is suited for the application that you want to use it and price. All these factors can be easy to find if you go to a good bike shop. Good luck!