There is no comparison. Katy Perry doesn't have the voice/talent to pull off a good musical performance, so she had to sell her soul to Satan in order to get anywhere.
Taylor is fun and obviously has a ton of talent, and I would see her concert any day and be genuinely thrilled. However, the question asks about voice and I think of Katy in songs like Unconditionally, and I feel her voice has more body than Taylor.
I'm by no means a fan of either of them, but Katy does have a much stronger voice and uses it better.
just a simple answer Katy Perry is was better
Katy has such a strong voice even though I love both of them
THERE IS A REAL DIFFERNCE BETWEEN THE TWO. Katy= Amazing vocals+Into season Taylor= Poor vocals+sooooo out of season