IMO, its both, they're as important as each other.
Bravery:
Does what it says on the tin, player will challenge with no fear, maybe help other attributes I suspect such eagerness to win.
Agression:
The player is a fiery character | or | Tackles hard but fair, BUT tackles very hard.
On my basis above then obviously it would be yes, but if I had to choose between the two I'd go for bravery, its seems to be the safer option, the other feels to gun-ho for me, not in a team game I want to play with eleven players not ten.