I've been using Tina's 4P+K and 6H+K, with the guaranteed ground throw of course. 6H+K does get countered on occasion, but it's rare and if it's only blocked it's a little quicker to follow up on.
Not actually got the costumes yet though because Pai keeps turning up in the later rounds and her AI is... well, beyond broken. She's the only one that ever beats this, though. Seems more consistent to me than Leifang's charge or Ryu's teleporting kick (both of which the AI regularly counters for me, all characters).