Question

Which value of capacitor is more effective as filter element, the larger or smaller and why ?

Answer 1

What kind of filter?

Answer 2

Capacitive filter, I want only the reason?

Answer 3

I would say bigger values of capacitors would be more effective. Since \[\ X_L = \frac{1}{2\pi fC}\]
where f - frequency and C- capacitance
X_c - capacitive reactance (capacitors' opposition to the change in AC voltage)

The smaller X_c of the filter capacitor with respect to the load resistance, the better the filtering action.

Also, if you have a larger X_c (small C) that means that there will be a bigger voltage drop on that element in the circuit, which you probably don't want.