Have both. Love both.
TSPP is way deeper...maybe too deep for the average guy (me). TAF is my all time favorite , probably because it was the first game that got me hooked on pinball. That said, you really can't beat TSPP multiball though when you have couch multiball, itchy and scratchy multiball and Homer D'Oh frenzy going on all at once. It's pandemonium.
Wait, I keep going back and forth. They're both awesome. Just buy both.