Masturbation is a topic discussed too little! What I use depends on the reasons I masturbate. Sometimes I do it just to relieve stress, perhaps sounds awkward but to me it can have a general soothing effect and for that I use porn to get me going. I tend to "get off" on porn which is not the kind of sex I normally have, so I guess it is a way of living out fantasies.
I have tried different types of online sex (chatforums etc) but generally I think it takes so much work to find somebody who is at the same level as you are so by the time you find somebody, the moment is gone. I guess it has to do with the unfortunate reality that there are like 10:1 ratio of men/women in the chat forums. So lately I have abandoned those completely.
Other times, I masturbate because I am simply just horny and then I don't need anyone external stimuli. My imagination works perfectly fine and I prefer to do it in the shower.