Most people will suggest getting started with either the Microchip PIC or Atmel AVR. I am partial to the AVR due to the availability of gcc for the AVR. Other than that, both parts are programmed by the parallel port in circuit and provide nearly the same assortment of integrated peripherals. There are certainly more reference designs for the PIC. From an engineering standpoint, I attempt to choose the most appropriate part considering the requirements in terms of connectivity, power, EEPROM, and development time.