The only thing that can penetrate a jadgtiger's armor is another kingtiger or something else with a gun that can penetrate 220mm of frontal armor. Sure, you could strafe a jadgtiger, but seriously, like I said, even the turtle, with side armor less than 100mm could sustain repeated superbarrages from british weaponry at point blank range.
It's pretty crazy for the end level tanks. I don't think the IS3 really compares too, as the gun isn't as good as an 88 and the armor isn't as good as the other assault tanks.
If I were to rank the top three best tanks, it would probably be:
jadgtiger > Turtle > kingtiger > IS3
The reasons would be:
Jadgtiger: Invincible and immortal. Long reload time, but ultra powerful cannon the likes of which no other tank can compare. Only weakness is tracks.
Turtle: Slightly less invincible but with a 4 second reload time. Gun is slightly less powerful but can still 1hKO a tiger.
Kingtiger: Super strong armor but ultra slow and a slightly less powerful gun. Easily strafed but unless they're packing a high level AT gun of some sort, won't die.
IS3: Well rounded, but takes forever to reload (15 seconds). Not invincible but not a pushover either.
Honorable mentions go to the Russian T-34 for it's amazingness, the German Stug for the overpowered frontal armor (it's an early game tank with 100mm armor for gods sake) and powerful main gun, and the goddamn American rocket jeep for being a complete pain in the ass with it's fast speed and penetrative rockets that can take down medium tanks with no trouble.
P.s: The US don't get shit for tanks. Their most powerful is a Pershing... gods. Pathetic. I think I'm more afraid of their rocket jeeps than their Pershings. Their infantry is powerful though, better guns.