choosing proper micro controller for your said application depends upon application requirements.
whether u require 8 bit, 16 bit or 32 bit processing?
what r the built in peripherals it needs like ADC, IIC, comparator?
what is the resolution of built in peripherals like 10 bit or 12 bit ADC, 8 bit or 16 bit timer?
ATMEL has series of AVR micro controllers while micro chip has PIC series to give strong compitition