If I remember correctly, it matters a lot exactly what the noise parameter is. As soon as things get noisy enough, Grim (start off cooperating, then defect if the opponent has ever defected) starts to dominate all of the clever Tit for Tat variants. Obviously, if you make things noisy enough, then Always Defect becomes the best strategy, but Grim does well long before that.
We had an IPD tournament with noise at our university recently, and I entered a variant of Downing (essentially, model your opponent as some sort of Markovian process) which won quite convincingly (mostly because it could exploit Always Cooperate, which was in the initial pool of strategies, better than the TfT variants).
If I remember correctly, it matters a lot exactly what the noise parameter is. As soon as things get noisy enough, Grim (start off cooperating, then defect if the opponent has ever defected) starts to dominate all of the clever Tit for Tat variants. Obviously, if you make things noisy enough, then Always Defect becomes the best strategy, but Grim does well long before that.
We had an IPD tournament with noise at our university recently, and I entered a variant of Downing (essentially, model your opponent as some sort of Markovian process) which won quite convincingly (mostly because it could exploit Always Cooperate, which was in the initial pool of strategies, better than the TfT variants).