What would you say is the relationship between Professor Xavier and Magneto?

ok so I watched Xmen: First Class when it came out a couple of weeks ago, and I really loved the movie, but it also got me to thinking how exactly Charles and Erik see each other. In the animated series that I grew up with from Fox kids, and all the movies, and especially the ending in First Class where Erik is the cause of Charles getting paralyzed but is very concerned for his friend, it seems that these 2 are not hateful rivals, they seem like brothers, but in the later movies and in some situations in the animated series, comics etc., they do seem to be hostile towards each other, so I ask you, how would you say their friendship is? is it a friendship? is it hate? a rivalry?