Sorry Cally, I don't know much about Road Helemts. Now if it was a choice between the Havoc and the Animas that'd be different! Doesn't the Giro website offer any pearls of wisdom? Or were you looking for personal experience?
You haven't defined what you mean by 'better' either. As far as the safety angle is concerned I think I am right in saying that Giro's are only certified to pass the EN - i.e. the same test. One may be safer than the other, but the tests don't give us that information.
Discounting safety then it just comes down to which helmet has the best venting, looks nice and feels good on your head. So you need to try some on really. Fit is the most important as helmets, like all safety devices, are not very effective if they don't fit properly or if you don't wear it due to it being uncomfortable!
Sorry for the rambling reply. I don't know the exact models myself as I don't wear a helmet, but I dare say they will both do a job.
The Atmos is the more recent model, which superceded the Pneumo as Giro's topline road helmet before the Ionos. Fit is pretty similar for both and performance-wise there's nothing in it - what colour do you like best? FWIW I've gone off Giro due to their poor quality and warranty support.
I got an Atmos this year - (was using a Met something or other) and I notice that it seems noticeably cooler - for my sweaty, hairless-ish head anyway - . Nice in red and black to match the Pro Race tyres too! Sad but true.
As mentioned there are a few nice looking ones out there - I also like the Catlike one, with the round vents - bit like a cheese grater...
I've got a Giro (something) that I use here in Vietnam although I bought it in the UK, and I find it's comfortable. The Rudy Project one I have at home in the Philippines is not so good IMO!!!!!!!!!!!!!!!!!!!!!!!!