I like to catch everything with a Pokeball, just to be "more traditional".
A normal Pokeball also looks better than any other Pokeballs, especial the Ultraball which has that ugly U on it.
Oh, and a last thing is, that you could buy 6 Pokeballs for the amount of Ultraballs that you are buying, which means if you bought Pokeballs, you'd be having more =D