HOLSTEINER!!! They usually listen better but thoroughbreds have more stamina. I have a holsteiner though :)) we event at beginner novice and moving up to novice soon:)
TB’s have WAYYYY better stamina and are typically better learners, but it’s a personality thing with each different horse and what level you want to do etc.
I don't think it really matters it depends on what the horse was trained for. Both are good for cross country it just depends what horse has more/or better training and who you think will take you farther
Both are about even for me