Which of the Capital Sins is the most grave?

I'd assume pride, since according to christian lore, that was Lucifer's down fall and it could be argued to also be man's downfall as well. I'd say that it's a pretty safe assumption to place most of man's atrocities under pride, as well. But, there has to be some pride, it's just about a healthy balance (whatever that is).

I would go with pride too. I remember watching some documentary about the deadly sins and how most, if not all, of the other sins could be broken down to basically be pride. I forgot the specifics but remembering thinking, huh that's a reasonable theory. And so pride it is :p

Avaritia. See, where as pride and wrath are irrational, engraved into one's soul such as being an aspect of you, of your personality. Greed is mostly conscious although maybe aided by an impulse, you choose to be greedy to want, to have, to take more than is adequate/necessary.The way I see it you can admire someone who is has a passion for their pride, glory, lust, wrath can you really admire someone who is passionately greedy? It is a fine line between Ambition and Greed. Though I guess you could say the same about sloth, gluttony, despair and envy. All sins can blind you, but Greed is when you put the blindfold on, not emotion. Atleast that's how I view it.

I think I agree with greed. We live in a world of capitalism, the world is basically run by greed. People who are rich always want more, prices are high to look after profit margins rather than people, jobs are mostly part time on contracts to save employers money...it's a pretty greedy world.

Well Betrayl is more of an act than a sin, it's the motivation behind it is what qualifies wether or not you are doomed to damnation. Hence "An act of Betrayl". For example: Do you think the American Revolutionaries are sinful for betraying their country and monarch? Was Jamie Lannister wrong to betray his oath and disgrace the kings guard when he ran his sword through the back of the Mad King Aeries? Ned Stark thought so. Stealing from a friend is an act of Betrayl but a sin of greed. Cheating on your partner is an act of Betrayl but a sin of Lust. Team killing your friend in a game for fun is an act of Betrayl but a sin of Wrath (Wroth).