You can say so informally (quiero hablar contigo) or(YO quiero habalr contigo) is a personal decision,
the two forms are correct, but the way (quiero hablar contigo)is used more when they know the person or depending on the intonation of voice is the form of tax and mandate, the way I want to talk to you(yo quiero hablar contigo) is more respectful and informal.
How formal it, can I talk to you (puedo yo hablar contigo), please let me talk to you, (porfavor me permites hablar contigo) are two of the most common forms and respectful.
I hope I have answered your question.
See U.