In reality, in captivity, those puffers are likely to top out more like 7-8", I believe in the wild they are more like 12". If you want a real puppy dog with alot of personality, the classic dogface is the tops, I have a yellow belly(here's a pic of my fatty). And yes I believe why the tank size recommendations seem small is because for the most part they are relatively sweety pies. I've always had one, even with some of my more aggressive fish, I don't know why no one ever bothered them. The stars and stripes puffer(Arothron hispidus) does get larger than the rest and likely needs a larger tank, I've seen them more than a foot, mine was a good foot, also a fun puffer. The 2 you listed above I would say their personalities would definitely take a back seat to the dogface.
I would personally advise against the angler, the best results I've seen keeping these guys, is when they are in a dedicated species tank alone or with just a couple choices of select room mates. Feeding them can be a challenge and ones being fed a dead only diet don't live that long, even with the best care mine never lived more than 3 years and no one I know ever kept them even a year. They are sedentary in nature, so they can be easily picked on by more aggressive tankmates, Their lure(esca) which resembles food on a fishing line will likely be chomped.
Thge Marine Betta is an awesome fish, not brightly colored but the shape, movement , and display is interesting. They are very, very shy, like nothing I've ever seen. Many times will have to start out on live food, unless you get one that was captive bred. And can be picky which foods they will take to. I really rarely got a glimpse of mine, sometimes I thought he had just died behind the rocks. then reappear fatter than ever. Figuring out their favorite foods can get them to come out more, they don't seem to like bright tanks, and mine really only came out under blue lights or lights out with ambient room light.