I choose them 1st for color and tail shape, and 2nd for personality.
When I was getting Saki, I saw a couple other beautiful guys, but they were so skittish and kept avoiding my finger and face. Saki was more calm and went up to my face. He was a greyish color with a lilac tint, which made me think he had potential, but his personality helped me choose him.
My other betta was color, hehe >.< I wanted a betta that could be as unique and beautiful as Saki turned out to be. Luckily, he also has a great personality. The runner up was more aggressive and less friendly, but Soren flared but not excesively, and he follows my finger and swims right up to the side of the tank when he sees me.
My husband picks the betta that "calls to him". He chose Sushi because he said there was jut "something about him". He was a royal blue crowntail when we got him, and there were 3 others just like him. But he wouldn't leave him there.
Shisu he chose because he said he reminded him of Sushi... which was a bad decision since he ended up being totally different and it disappointed him. He gave him to my daughter, and got a new one.. that I think he chose this time for color, and this one has a great personality too, so that's a bonus! He spent 5 minutes staring at him this morning because this new betta grabbed a piece of food and just swam and swam and swam while holding it in his mouth for the whole 5 minutes... longer, but he got tired of watching the little guy, lol.
Saki - color and personality
Soren - color
Sushi - personality
Shisu - ? reminded of sushi?
New guy - color