Some hairstyles are not suitable for helmets and a few of them are :
- Hair buns because they are big and you can`t put your helmet on.
- Curls and teased hair because this hairstyles would get crushed so you wont have those gorgeous curls or volume anymore. In short its not good because you get crushed curls and no volume
- Wearing your hair down (free) its not good because (at least for me it`s not) it gets tangled and then its really painful to go and brush through them.

And for me the most suitable styles are :
- Braided hairstlyles yo could literally do million styles with braids.