It depends what you mean by "sound better". A higher tuning frequency will typically lead to a louder sound with a loss in sound quality. A lower tuning frequency will have better sound quality with a loss in output.
For that sub there really isn't too much of a difference between 28 and 33 Hz tuning. If you are looking for the best SQ then go to 28Hz. If you are looking for the most output then go to 33Hz or slightly higher. If you want something in between you can go in between those two values. Again, the difference isn't much in that range so it won't matter too much.
Good Luck!!!