well, the greybeards gave u a couple of shouts and will direct u to a word wall, and alduin wil give ya a choice between 3 perks
Blades found u an awesome hideout, lets u recruit 3 followers and boost thier stats and keep them in 1 place, u get a perk, u get a temporary perk, armor, and unique weapons, and direct you to where dragons are.
Shout anywhere wheres theres people and u get a letter directing u to a word wall.
talk to innkeeper in riften and u get a dragon location.
So boils down to
greybeards--2 shouts, and paar gives ya a perk
Blades--hideout, armor, weapons, perk, temporary perk, raises stats of followers that are recruited
So ya get more from blades but ya gotta kill a dragon with a cool voice.....u cna do it, it aint that hard, trust me
, u never know u might find out later u saved humanity..or doomed it...