First of all, other than Three Days Grace, none of the rock bands you named are considered or ever will be "hard rock". Those bands are more metal bands (and Bullet for My Valentine ******* blows). If you actually want to get into some real hard rock n' roll might I suggest Clutch, Priestess, King's X, The Cult, Masters of Reality, Eleven, Pride Tiger, Wolfmother, Stereophonics, Burning Brides, Queens of the Stone Age, Led Zeppelin, and Deep Purple.
Second of all you cannot generalize that all rock is agressive because there are many subgenres of rock such as alternative rock, emo, grunge, indie rock, punk rock, etc. which do not necessarily center aggression.
Third of all there is no better genre, pop or rock, they are both good in different ways. They are also very similar in some aspects as well.