How important are both these attributes?

I just got a CB regen will low aggression, is this gonna prevent him becoming world class?

Or will he choose his tackles better and not dive into challenges?

Opinions?

Just means he won't keep getting sent off. Mental attributes of youngsters tend to increase anyway with experience although I can't remember off the top of my head whether aggression does or not.

I would be looking for both Aggression and Bravery in any Center Backs I'm wanting to sign.

I find that if you sign players with very high aggression (18,19,20) then you're asking for trouble. They get sent off far too often, but on the other hand you probably don't want to be stuck with a player who has anything under about 10 there either.

Probably more important is positioning and anticipation.

aggression is key for my DMCs. but Flamini used to get sent off everytime he returned from suspension, 4 in a row at Athletico. i don't think his agg rating was that high, bravery might have been.

strength, positioning & concentration key for my CBs.

I'll agree with looking for high bravery for centre backs, but personally, I'm not to keen on having too high an aggression stat for them, as it could well lead to the layer giving away free kicks and penalties in dangerous positions, and increases the risk of the player getting carded, which, could be costly for centre backs, especially if they are the last man.

Bravery - essential for a CB - you don't want him pulling out of challenges now do you?

Aggression - everyone seems to be interpreting this the wrong way - according to the games manual (and users in the T&T forum) this refers to a players willingness to get involved - e.g. steven gerrard will quite happily motor about the pitch and try to cover all, hence a high aggression, whilst the likes of anelka are a tad lethargic, hence low aggro.
It does relate to dirty challenges as well, but not as directly as everybody seems to be implying.

Similarly, if a CB has high aggro, it isn't an issue as long as his tackling ability is high - as high aggro will cause him to attempt more tackles.

Or at least this is my understanding of those 2 stats.

Bravery is way down the list of stats I look for, even more so aggression, though I might be concerned if they had a really low rating.

Aggression, I tend to stay away from the extremes of, in both directions. As noted earlier, 18-19-20 Aggression seems too prone to picking up cards .. but on the other hand, I don't want a docile player, either.

Bravery, I tend to find that as long as its "reasonable", say 9+, 10+, its not an issue. Its the really timid ones (1-2-3) that have trouble. I had a goalkeeper with a Bravery of 1 and it actually looked like he was ball-shy.

none GK should actualy have bravery 1, lol