For me this depends on the context:

1. On the first message of a conversation I prefer a wall of text, because that lets me read all of the details really quickly.

2. If the conversation is likely to be short I prefer the one message after another since my attention is already on the chat, and I might as well be reading what they're typing rather than watching the "x is typing..." indicator.

3. If the conversation is going to be long I much prefer a call, I don't have the time to wait for someone to type all day. Context switches are expensive so I don't like reading occasional long messages while I'm trying to work.