Fashion!
If you are after a helmet, then just look and see what is comfortable, fits will and feels right
Secondly where possible look at the standards it has passed, preferably look for a Snell certification as these helmets pass a stricter and tougher range of impact tests than other standards
If it only passes EN1078 avoid it!
Specialized helmets do nothing for my head shape.
Specialized helmets do nothing for my head shape.
They'll all be built to the same standard so use the one you have or buy one that you like and that fits or don't wear one at all.