[Jebdm]

I mostly prefer text-based conversation. You have more time to respond, there's usually less filler, text creates an extremely convenient/useful record automatically, it is easier to return to past topics, it is easier to communicate bigger/more complex ideas, and (for me) reading is quicker than listening.

The only real disadvantages are that typing is a little slower (I type around 90 WPM but speak around 150 WPM) and that you don't get body language cues in writing. For the sorts of things I am interested in, though, I actually prefer not having body language. Body language makes us try to react to others by guessing their mental states from some subtle changes in their shape. This is problematic for two reasons; first of all, this sort of guessing is inherently imperfect, but more importantly, we tend to be quite heavily influenced by our perceptions of others' reactions. (This makes sense, evolutionarily; it is a way of making us cooperate and preventing us from diverging too much.)

What this means for conversation is that topics are chosen, opinions are suppressed, and minds are changed purely on the basis of our faulty readings of others' opinions. This is especially problematic when talking about abstract ideas because subconscious emotional reaction is an awful predictor of the merit or validity of ideas. The problem is compounded because we are very bad at simply setting aside our reactions, especially in social contexts.

Body language heuristics are obviously good for some things. They help us negotiate relationships, know when others are upset, and interpret ambiguity. But they also give us false impressions and lead to socio-cognitive biases. Furthermore, a large proportion of the benefits of body language come from dealing with problems of face-to-face interaction between primates, meaning that the benefits are less when dealing with textual communication (and especially communication about abstract ideas).

Even small talk over IM seems to be more stimulating to me on average than face-to-face small talk. I have observed this not only in my own interactions but in watching the interactions of others as well. My sample could be biased, because I am obviously a nerd who mostly hangs out with other nerds, but I think I've seen enough "normal" people to make a general statement. Your mileage may vary if you have different tastes in conversation than I do. But if you prefer to talk about the abstract or the complex, or if you try to avoid cognitive biases, then the only way I can imagine face-to-face conversation being generally preferable is if it has a strong instinctive appeal to you.

A lot of people do seem to have this innate preference. The same people often seem to prefer reading on paper than on screens. Some of them say their preference is based off of eye strain--which might even be a reason to prefer speech over text--but for a lot of people the reason seems to be more aesthetic.

[TikiTDO]

There are some other very important advantage of text that I feel you omitted. First, the ability to simultaneously carry on discussion on multiple topics all at once is a huge factor. In a normal, face to face conversation following an interesting but unrelated line of thought can sidetrack the entire conversation, often beyond the point of recovery. When you move to a textual medium you can easily carry on two or even three topics provided that both sides can keep track of the various conversation contexts all at once. Best of all, you can follow up on these branches in conversation even while the other person is typing.

That brings me to the second huge benefit. When talking, you will very rarely speak at the same time as another person. Not only is it rude in basically all cultures I am familiar with, it also makes it hard to follow what either person is saying. With text there are no such limitations. When you consider that an average person can read up to 300 WPM, while someone that has practiced speed reading can easily break 600, it is not too infeasible that both sides of a conversation may be typing the vast majority of the time. For those well practiced in text-based communication this can greatly increase the average amount of information transfered per unit time, easily negating the difference in typing vs speaking speeds, and possibly even improving upon it.

I do agree on your notes about body language and emotions. I have lost count of the number of times I have seem people interpret sarcastic textual statements to be completely serious. On the other hand I find that people get better at recognizing even that when spending enough time reading chat/comments online.