Might well stick DEF cards on everyone if the gameplay turns out the way everyone says BB. With what's been said about the 1st touch its looking like guardian cards all round...
Kiwi, don't be surprised if the in game stats show no difference, they've taken pains to point out that there is no way of finding how the boosts work exactly. Why this should be is a fine question.... IMO, DEF should give a strength boost as it definitely has a big impact on the card stat.
Balance and agility also have an effect on the dribbling stat so I'd think about PAC + DRI for a boost to those 2....