Shimano's Deore Front Derailleur features wide pivots and a rigid cage for awesome shifting and top-notch durability. Made for triple-ring set ups, it's 10-speed compatible. It's a dual-pull, so it'll work with any cable routing, and its design gives you better rear tire clearance.
Capacity is calculated by subtracting your smallest chainring's tooth count from the largest chainring's tooth count. Example: 46/34/24 chainrings: 46 - 24 = 22-tooth capacity.
Bottom-pull derailleurs are used when the cable is routed underneath the bottom bracket and up through the cable clamp. Top-pull derailleurs work with frames where the cables are routed down from the top tube.
Your seat-tube diameter determines the needed derailleur clamp size.