Uh, generally I'd have to go for speaking, but the dialogue needs to be well constructed and the voice acting good. Dialogue doesn't ruin the immersion, even if its someone elses voice I can still think my way into my characters shoes. The Oblivion motto of "live another life in another world" comes to mind. (an odd example seeing as your character is also bizarrely silent in that adventure too, but Fallout 3 was made by the same people and I enjoyed it more simply because of the dialogue options.) Silence actually harms immersion for me by limiting my interaction with the game world. For example, in Fable 2, you get a couple of expressions and other than that the character is completely silent. I'd rather have long dialogue trees than wierd silence. Imagine if you could actually barter with shop-keepers for lower prices, flirt and develop relationships, and hold developed conversations with flexible conversation options. Sounds a hell of a lot better and more immmersive than flexing your arms till the prices (and pants) drop. However, silence is better than really bad, repetitive dialogue with rubbish voice acting, and it is better for your character to keep his mouth shut and be thought an idiot than to open it and remove all doubt!