We have a tie. 22-22.
Mask of the Phantasm
Under The Red Hood
We have a tie. 22-22.
Both are excellent 5 out of 5 stars, however, I slightly prefer Under The Red Hood simply for the scene between Bruce, Jason, and Joker; so much powerful emotional baggage goodness.
"So you've come to the end now alive but dead inside."
I much prefer UTRH's animation style and consider Jason a more interesting antagonist than Andrea. On the other hand the music in MOP was outstanding and that scene where Bruce visits his parent's grave's to try to back out of his promise was epic. Two great movies. Overall I do prefer under the red hood, it is very close.
You can't really make Helena a love interest for Bruce. Well, you could, but that'd probably be a very bad idea. And in fairness, she exited in a canon where Huntress wasn't around yet (not until JLU, and there she didn't interact with Batman much), so she wasn't that redundant.
I like Andrea because we are kind of starved for competent, interesting female Bat villains besides the big three and Talia. She might not work beyond a one-and-done story but I'd be interested to see if a writer could still try to make it work. I also don't care that much for Jason and saddling Bruce with dead kid baggage, so I think more inclined to favor Andrea by default.