I'd chose Latias. I like that more "carefree" nature. Though Latios was pretty cool in that ONE movie I will never remember the name too. Pokemon Heros, I think it was.
Competetively, yes- Latios has a higher Sp. ATK stat. But, Latias with one or two Calm Mind Boosts- unless you have Pursuit or something dealing super effective damage to her defense stat, she'll never fall out of the sky. Especially with Recover.
And her Sp. Atk stat is quite impressive afterwards.
So, yeah. IMO, Latias. :3