I don't know, the more I think about this, the more I think you need to approach the 2nd ball break with a degree of caution. If you're on a table where it's unlikely you'll run out (either because it's you or the table), then hitting the second ball is a great way to go. If you're nuking the rack and getting great spreads, I'd go with that. As a 6, I understand you might feel like you can run out the entire set some days and when you're having a day like that, you should ride it.
I am torn on the 2nd ball break and find myself going back to the first ball from time to time. A scratch on the break is always a reminder that there is a big risk.
The thing is I have gotten pretty good at the 8ball break. Winning a game in one shot is too big of a advantage to ignore. I will add the disclaimer that I only break on the 2nd ball in league and tournaments.
On another note, I had a chance to play Dan Louie a couple weeks ago and he was breaking on the 2nd ball in 8ball. He made the 8 once and spotted it (probably going by BCA rules). I have to think he was doing it for some reason. Of course his break is a lot better than mine and he was making a ball on the break every time.