Generally speaking, the decompilation of any machine level executable is an undecidable problem (it's equivalent to the Halting Problem on a Turing Machine); so an ultimate answer to this problem cannot exist. I've heard about top secret discompilers that would be able to perfectly reconstruct many C sources, but I guess that it's all hearsay.

IMHO, it's possible that in selected cases a good result can be achieved, and this could be the case of Micro-Processor Services, as they offer different versions of discompilers, depending on the peculiar assembler that has generated the machine level code; and, above all, their products can translate ONLY assembler generated code, not compiler (high level language) generated one.
Anyway, how many programs are entirely written in ASM? I think that these programs are of limited use in reverse engineering practice.