Best Lamp Dimming Circuit?
In general for dimming a lamp following is applicable.


Make the amount of power going into the lamp variable
Prevent as much as possible the loss of power in the controller


In many domestic dimmers using mains this is done with a triac or IGBT controller.


The triac controller makes that an adjustable part of the incomming mains voltage is transfered to the lamp. Leading edge phase cutting.
An IBGT controller can operate with leading edge and trailing edge phase cutting.

Now if you replace the lamp with an LED device than the preferred methode of dimming is to rectify the incomming voltage and feed the DC voltage to the LED device in a chopped manner. This is called Pulse width modulation. 

In some expensive dimmers one can preset the methode of dimming making such a dimmer suitable for Halogen lamps, LED Lamps with buildin electronics both trailing and leading edge modulation, CFL lamps and so on.