Another reason to get Manga Studio, ooo! I have Illustrator but I've yet to play with the balloon/bubble tools. Gotta get in there.
Now, in Photoshop, since it's habitual at this point, I use the transform/warp tool to pull the nodes and get the shape I want. It's... much faster and cleaner than trying to eyeball it but still not as efficient as MS. I'll share what I do just in case anyone's interested.
First: some simple marquee fill balloons and text.

Second: Select the balloon to "warm" with rounded corners and Edit>Transform>Warp
Third: Grab the innermost nodes (they'll be little black bullets) and pull directly up, keeping the guideline as straight as possible (really helps to zoom in!)

And viola! It's nice, much more pleasing to look at than before and it only takes 3 or 4 seconds per balloon.
It's really up to how square-ish you want the balloons to look, too. It's exaggerated with these but it's super easy to just slide the nodes up and down to get just the right look you want.