Alright, let's put some feedback to this thread.
The bottom one seems to be installed by SimplePortal. While making new layout, I already discovered the shoutbox is not mobile friendly and tested the SimplePortal's shoutbox.
Well, I don't make detailed testing to it, however I found a bug while trying to fix the homepage problem: http://simpleportal.net/index.php?topic=13932.0
About the top one, I can say that it works, but the way it works, and how is it coded is not very pretty.
First and biggest issue to me, the developer don't made a stylesheet for it. Instead it embedded styling info to the source code instead.
On SMF, you can actually change how stuff look using template files too. And the developer again, put the most of the actual code to the template file.
It's a big pain to locate the style codes and change them to me.
Second, It actually puts server on stress.
Unlike most of the forum, shoutbox needs to be constantly updated so everyone gets new shouts without refreshing.
There are several approaches for this. Here, I list commonly used ones here. Shoutbox uses the 1st one which is the worst approach.