I think strength training is more important. Becoming strong makes you more mentally astute. The brain and body are totally connected. Plus, if you are genetically predisposed to being weak, you can counteract that easily with strength training. If you are genetically not very bright, there's honestly not much you can do. You might as well become strong. If you are naturally intelligent, there's not much you have to do to stay intelligent. You'll naturally seek out information and learn. The internet makes this incredibly easy.