I don't recommend the knuckle ball unless it's a last resort.
Major League clubs don't use the pitch unless it's the last option for a guy before he's released, which usually happens at the end of a guy's career anyways. (And even then, the player has about two-to-four weeks to show he can throw it, and not a day longer.)
Tim Wakefield was a position player first, who was on his way out the door before being converted into a knuckle ball pitcher -- a last resort that worked. But he's the exception to the rule.
In the Majors, where the average pitch velocity is 87-88 mph, the knuckle is thrown at 65-68 mph. Any harder and it doesn't knuckle. Any slower and it basically doesn't reach the plate.
Another guy that comes to mind is a pitcher I played with in pro ball I, who was getting rocked on the mound. So Cubs brass sent him back to the Cubs Spring Training facility in Mesa, Ariz. to work on his knuckle ball. While there, the coaches made him throw it at 66, 67 mph. After a few weeks -- when they'd done what they could with the pitch -- they sent him back to a minor league team. He pitched one game, got rocked, and was released the next day.