Olimex - The European board producer summed up the ARM with this statement:
PLUS:
Very fast: most ARM7 cores run at 60Mhz and ARM9 cores run at 150Mhz+ providing more power than old 386 Intel processors.
Low power: ARM7 cores need only approx 0.5-1mA per Mhz
Great range of peripherials: ADC, DAC, USB, SPI, UART, I2C, CAN, Ethernet, SDRAM.
Lot of internal Flash: 32KB-1MB, Lot of internal RAM: 4-256KB.
MINUS:
too complex to beginners, definitely this one should be not your 'first steps in microcontrollers' 