GPA, they ventilate very well and are super comfy
i absolutely love both. there are pros and cons. gpa and samshield both have decent ventilation, although gpa may win on this one. as of price point, samshield is way more affordable ($400) than gpa ($600). samshields have a lot more of a hunter/eq look on them, and gpas are more popular in the jumper ring. it really just depends on what youre looking for in the helmet.
GPA is very well ventilated, but the Samshied is way more protective, so its up to what you prefer😊 Hope that helps!