I have been wanting a 29 gallon for a sorority so personally I would use the 30g as a sorority tank (12 - 15 females) and also put the Cories in there because they would be happier there than in the 10g. I would add one or two more Cories of the same type too (if they are different species they will not shoal together) because I hear they are happier with at least 4 or 5. I would plant the 30 gallon heavily with live plants, both to create hiding spots for the females and to help with the water quality in a slightly-overstocked sorority tank.
I would use the 5 gallon tank for a single male betta and nothing else. Or, maybe divide it into two 2.5 gallons and get 2 male bettas.
The 10 gallon you can do a lot with too...you can use it for a small sorority (5-6 females), divide it for male bettas, or use it for creatures other than bettas (I would really love a shrimp-only tank right now, they are so cool!).