Kiri is the only big name opera star, I have never seen or heard in person. A few years ago, I was in Vancouver and saw a poster for her farewell concert and reading futher, I discovered I was two days too late.
I love the character of her voice. There are (were) other sopranos out there, but her voice had such a wonderful quality and richness. Others are ok, but come off to me as a bit too shrill.
For me vocal character is key. Pavarotti was a magnificent tenor, and he could hit those notes with accuracy and clarity. But I prefer the warmth of Bocelli's voice over his, even though he lacks that accuracy and throws is that occasional (almost imperceptible) flat.