Which is better GHz or MHz?

MHz and GHz
MHz is short form Mega Hertz and GHz is short form of Giga Hertz. Hertz is usually the unit of frequency measurement. It indicates the speed of the computer’s CPU or of any other component whose performance is given in terms of frequency. Generally, higher Hertz indicates faster performance

1 MHz = 1,000,000 Hertz (1 million Hertz)
1GHz = 1,000,000,000 Hertz (1 billion Hertz)

CPU speeds

The speed (operating frequency) of the CPU is measured in megahertz (MHz) or gigahertz (GHz). The higher the value the faster the CPU will operate. The original IBM PC released way back in 1981 ran at 4.77 MHz whereas modern PCs can run at over 4000 MHz, which gives you an idea of how far things have progressed.

1 MHz means that the device will run at one million cycles per second. 1 GHz is a thousand times faster, so that 1 GHz = 1000 MHz.