Text-based. Past that, it matters not. Phone SMS message, AIM, e-mail, forum, whatever. As long as it is text-based.
Phone conversations... hate them. Feel awkward. Rarely initiate the phone call, reluctant to answer one. Various reasons for this, that's unimportant.
Face-to-face, again, not preferred. Hate eye-contact. Miss some queues. Over-analyze some others. Don't always know what to say, or when to say it. Not a fan.
Text: Not real-time, even if it is "close" like AIM. Gives me time to process my thoughts and try and come up with the "best" (in my mind) way to respond.