it's a strange issue, and one that opens a lot of other similar issues. the 2 things are almost impossible to fairly compare imo. the entire history of the shield is based on its unbreakability. when the shield is damaged or broken, it is usually associated with some sort of major event--it's one of those 'holy f***' moments that indicates there was a massive power used. i think the shield has actually been nerfed in recent years, but that's just my opinion.
in contrast, if g's armor is damaged, readers (at least myself) take it in stride. it isn't a means of defence, as much as it is a costume, or containment suit. has it withstood greater cosmic forces than the shield? yeah, i think that is safe to say. the best feats for the shield i can recall off-hand are withstanding krona's blast (i think it was krona who blasted kal when he had it, and the same krona who beat down galactus (did he wreck g's armour in his attack?)), and taking korvac's power (iirc) in the avengers. i'm sure there must be others but for some reason i can't think of any.
still, g's armor has been through greater battles (like the beyonder) and survived. but again, not sure it's a great comparison. the armour also keeps him from appearing naked, so it will always survive. like hulk's pants. 😄
galan made some great and fair points in that other thread about a desire to compare higher durability feats and there WAS an awful lot of dodging by several people when he asked for the higher order comparisons. but is g's armor based on his power levels? the armour is certainly thicker. too many variables. the shield is renowned for its durability. g's armour is not. that of course doesn't mean shield>armour but the shield does not suffer from all the variables i mentioned. if push came to shove, i would say the shield is likely stronger in general, but given the nature of galactus himself, i see no reason to think the armour can't fluctuate in levels and we can't dismiss the high showings of the armour to survive conflicts that would likely have destroyed the shield. i just tend to see that as more related to the nature of galactus himself, than the armour in particular. if that makes sense.