The ATMEGA 8 can sink up to 20mA and source up to 10mA.
In spite of that fact, I would suggest You to use an N-Channel Logic Level FET Transistor or an NPN Transistor.
Because you can use it for higher Supply Voltages, when connecting more than one LED per Channel in serial manner.
With a PNP Type ( or P-Channel FET )you had to use an additional Transistor to drive the Power Transistor when the Supply Voltage for the LED's is higher than the Supply for the Controller.
Usually P-Channel FET's has an higher RDS-on, that increases the thermal charge of the Transistor.