why three phase circuits better than two or four phase ones?????

Answer 1

There is no such thing as four phase. Two phase is obsolete. The main advantage of 3 phase is constant power delivery. A single phase of AC power, the instantaneous power changes with voltage and current (goes to 0 when the voltage crosses 0). The 60W of your light bulb is average power. With 3 phase, the instantaneous power in the sum of the phases is a constant. This makes motors and generators run smooth (more efficient). Two phase was an improvement over single phase in this respect, but not perfect like 3 phase.

Answer 2

Three-phase electric power requires less conductor mass for the same voltage and overall amount of power. It has all but replaced two-phase power for commercial distribution of electrical energy, but two-phase circuits are still found in certain control systems