I mean, there's definitely a good argument that V8 is most advanced, but, for example, JSC is the only one that has the LLVM 'fourth tier', and it shows on asm.js benchmarks, where it mostly beats V8 (loses to Firefox, but that has asm.js-specific code while the others don't):

http://arewefastyet.com/#machine=29&view=breakdown&suite=asm...

So I think the question of "most advanced" is basically subjective.

Don't get me wrong! I would strongly prefer if iOS allowed any JIT to be used. I just think calling the one that can be used "most advanced" is not wrong per se.