Are you a casual player?
Whether flight sims are you favorite games or you are just learning the genre, is a major factor in your choice. If you are new to flight sims, your best bet would be to start off with a joystick and see how you like the games. If and when you decide you really like flight sims, then it is time to consider buying a yoke.
The majority of us are on a budget, so price is an important factor when considering buying a yoke. Chances are you can find an inexpensive joystick. Just remember you get what you pay for. Higher-end joysticks, can be as much as a cheap yoke. High quality yokes can be priced at $200 or more, and are usually found at specialty stores.
If your favorite flight sim doesn't support a yoke, there isn't a point of having one! Make sure you read system requirements, before making a purchase.
Consider your all your options. If you truly enjoy flying with a joystick, stick with that; you may not enjoy using a yoke. For this reason, you might wants to consider buying a cheaper yoke, before spending a lot of money. Whatever feels right to you, is what you should fly with.