Which is exactly why I prefer text to be in a text box and high contrast - light text on dark background or dark text on a light background. Besides not being able to tell who is talking, the other issue that floating text has is that it can blend in with the background and disappear completely for me.

What comic books do you read? Usually it's very clear. There are several techniques to guide the reader.
Of course first of all you follow the panels from top left (manga from top right, japanese read from the right to the left).

Then you follow the bubbles following the closest one to the character, these can go over multiple panels if there is a conversation happening. They bubbles of two character can also be placed alternating, making the conversation look like this:

(characters)
| |
A |
| B
A |
| B
A |
| B
A

If there are more than two chars speaking the other bubbles usually follow the general direction of the conversation.

This creates some dynamic with also the option of one interrupting the other without needing another panel to display it.