1- Any movement in which your body is moving through space rather than the weight moving through space with your body remaining stationary... is better. EX: chins will always be better than pulldowns.
2- Weighted chins and dips are fantastic muscle builders. They don't shape or give any illusion of any kind. They are simply efficient strength builders much more so than cable pushdowns or cable rows.
3- Reps are important, but not very important. There are 250lb super lean bodybuilders on this board. Some lift in the 5-8 range, the 10-15 range, the 15-20 range, etc. When it comes down to it, the payoff only comes when your food, rest, and healthy supplementation are in check COUPLED with consistantly trying to beat your logbook. Most of the huge guys on this board who win shows are brutally strong and are the most consistant. Look at Shelby Starnes, Dusty Hanshaw, Phil Hernon, Homonunculus, Brad Davis, Mountaindog, etc.