The eyes on the first one look red to me on the commercial

 

It is hard because I haven't read the comics in 30 years, and the "final" Megatron is so iconic now. To me the traditional head is just more distinctive, and the more uniform coloring with the gray helmet looks better.

 

I like both heads, because of the lines on the face I personally view the black helmet as Megatron in his younger days while the silver helmet as old Megatron

 

The first one is young Megatron. His head got damaged in one of his battles, and then he changed his helmet to a bucket.

That is my head canon.

 

The original head makes a great shattered glass heroic Megatron

 

The original design is more what the character was supposed to look. Back then toys were often designed with parts that you were meant to ignore, because they couldn't design it better. The Grey thing on top of toy Megatron is there because it goes nowhere else, not because it is meant to be part of the head design.

But I find it clever how they took this Grey part and redesigned the head completely and change to proportions to make the Grey part the helmet instead of the actual black helmet which then only gets referenced as the black "brows" on cartoon Megatron. The redesign made him look better than he was supposed to look.

 

do you know if there is more info about how the designer changed the look?

 

Just what I was going to point out. The whole head and helmet on the G1 toy are inside the grey covering part - a bit like (but not as noticeable) as Motormaster's head and helmet are inside his sort of block surround hood.
What we know as Megatron's 'eyebrows' were supposed to be the top of his helmet.

 

The original design is a horror revelation trope, in terms of the evolution of the story, and as the episodes go along. The final design meant that Megatron could remain a permanent Optimus Prime foil

 

I've always thought the final design is a bit cursed because kibble his head was nestled inside was reinterpret as a bucket head, while the top of his actual head (which also looks like a helmet of some kind) became his iconic "eyebrows"

his actual toy head looks somewhere between springer and apeface.