When it comes to speech bubbles I try to play around with them to make them fit the composition of the panel/page. It's definitely the weakest aspect of my work (at least in my opinion.) But as I'm currently working on my 3rd 100+ page book, I've gotten a bit of a feel for it.
Speech bubbles like the one in the picture you posted, is something I personally avoid like the plague. I hate them so, so much. Big blocks of text I prefer to break up into multiple bubbles, and maybe even across multiple panels.
An example of Trespasser Chapter 02 is this. I broke up the text, and staggered the sentences to make the whole look more appealing and have it fit within the overall panel:
My style has also pretty much gravitated towards longer horizontal balloons with no more than 2 lines of text within a bubble (though exceptions apply.)
As a tip, when layouting the composition of a page, start with the text first. I find it easier to fit my art around the words, than the other way around. If you look at the earliest pages of Trespasser you'll see me making that mistake haha.
Finally, as for punctuation, I kinda always have a since sentence within a single balloon, so there will always be a point, question mark, exclamation point or an interrobang at the end. (not me now noticing I literally forgot a point in the Buntha Bear example )
In some cases there's a group of three points if the the sentence continues in a different balloon.
An example from Chapter 03