Hard to say. According to the numbers crunchers guys, the panther was all round better, and I mean that literally -- faster, better protected (yup), and harder hitting (yup again).
Surprised me too, but that's what the guys who point out armor sloping and muzzle velocity and all that good stuff say.
Despite that, the Tiger has this rep of being the stronger tank, the Panther being the speedier. I tend to respect the opinions of the guys who put their time in with the vehicles (or fighting against them), so that would be a reluctant vote for the Tiger, but then again the numbers, as they say, don't lie.
This stuff is so complicated. For instance, the Russians did tests on the Nemetz (German) vehicles, and they found that, though the Tiger II's armor was thicker and better sloped, it actually was of such poor quality steel due to late-war shortages (and problems with the Swedish supply) that the Tiger I's armor was all-round stronger and more stable -- less likely to crack when hit, etc. There were photos to go with the report and they show this horrible shearing away of the softer steel used on the Tiger II when it was hit by a large caliber Russian round, whereas the Tiger I armour just stays together better -- it's really obvious from the photos.
Hey, don't hit me, I'm just quoting the Russians!