To be an effective martial artist, you need 3 things, to be fit, to know your techniques accurately and to have experience. For example, you can be a black belt in Karate and practice strictly by doing drills, such as no hitting below the belt, etc. but on the street, more often than not, that same black belt is going to get his a$$ handed to him on the street. Now, if you are practicing Kung Fu for fitness and for fighting, then almost any martial art style will do. There are some styles that will mess up your health, such Prey Mantis and Muay Thai, depending on what level you are practicing at. But since your focus is fitness and not fighting, you just have to practice your techniques accurate and regularly and you will slowly become fit, depending on how often you practice, you don't need experience.
If you are doing martial arts for fighting for whatever reason, then you need all three and you are better off practicing several styles because each style has its own strengths and weaknesses. For example, Wing Chun's weakness lies in the fact that you must be very close to your opponent, meaning that you must fight your way in. Against a style that attacks and injures anything moving, such as your arms and legs, this will mean that by the time you get in close to use a lot of your techniques, there are going to be several bruises, cuts or even ripped flesh on your arms and legs. An effective style to use against Wing Chun is Tiger Fist or Leopard Fist. Also note that just because Wing Chun completely specializes in close range combat doesn't mean that its going to win over a majority of styles, that is a hybrid between far and close combat or strictly far combat, in close range combat. Someone very good experienced in Tai Kwon Do, a ranged style, can still win over a Wing Chun practitioner in close range combat if they know what they are doing.
ChunLi