Krypton had superior technology, but Zenn-La was a far more Enlightened World. Each planet had their different strengths. Despite the Silver Surfer's far greater access to the reaches of his Universe, I have to go with Superman.
The Silver Surfer has traveled thousands of worlds, but hasn't learned much from it. His emotional landscape has been tested, and his connectivity to the universe has expanded, but Superman has done more and gained more intelligence with less exposure to his universe.
Superman is more intelligent.