At least the same- The firefly IS still a sherman. The 17-pounder isn't some magical wand that deflects' 88mm shells. The Firefly's survival depends' upon getting a first shot, at about 500 yrds. to be sure of a first-round kill. Otherwise, the Tiger's first shot in the engagement will be the last.
The Comet's armor might let it survive at a closer range to a Tiger than the Firefly could.
BTW, Why is this in the O'club, and not Planes' and Vehicles?
The Tiger has surplus killing power against either, Choose speed or killing power, in history killing power trumps speed.
Neither tank has the ability to go one on one with Tiger with confidence. Both can easily be defeated by the tiger but cannot be sure of returning the favour at longer ranges.
The Sherman has a better chance of killing the Tiger at a range that it might resist the 88mm hit. The Comet might be missed by the tiger because of its speed, but would have to count on a few of those to threaten the tiger.
Given the choice, I would take the higher chance of killing the tiger with my first shot.
Against a panther it gets worse for the comet.
So I will take the firefly, I suspect most would if the comet was introduced.