I think both are very good actresses. Who one prefers is only a matter of taste. Michelle herself on Anne:
"Oh, I think she's great. I'm actually very much looking forward to seeing her in the role. I'm a big fan of hers and I think she has everything you need for that role. She has the humour, she can go to dark places, she's obviously very talented. I think she's going to be really good."
And she was right
Also, having just watched Les Miserables a week ago, Anne definitely deserved her Oscar. Acting wise the "I Dreamed a Dream" scene gives off the same level of heartbreaking despair as Michelle's post-revival freakout scene in her apartment, and she does it while singing.
And having just watched Batman Returns a few days ago, Michelle Pfeiffer's performance really
is incredible and shouldn't be taken for granted.