lets say I have a bunchful of stalwart weenies (follower, sentry, royal guard) in play and valar kills them all. obivously I'd like the stronger ones like eddard and ser-dies-a-lot-condon to be on top of my deck. what decides the order they are on the top of my draw?

You do. Note that this applies to all moribund cards with a common destination, whether they're moribund because of a single effect or multiple effects in the same action window.