ORIGINAL: DaveFlynn
Both higher capacity an higher C ratings add weight. There are several trade-offs involved. For example a 1000mAh 30C battery would give you top performance, but wouldn't last long. A 3300mAh 10C battery would give you long 2D flights, but may be too heavy for good 3D. The most popular and therefor least expensive is the 2100mAh, 16C to 20C. At 5.5oz they're a good compromise between weight and capacity.
Excellent post Dave, I did forget to mention weight in the equation.