What is the difference between ATmega8535 and ATmega8535L ?

Which one is better?

 

Have you tried reading the datasheet and finding the difference?

 

Read a datasheet...genius ha ha

Its on PAGE 1 of the datasheet.
L=2.7-5.5V operating voltage and 0-8Mhz speed
no L = 4.5-5.5V voltage and 0-16Mhz speed

 

It is also a quite open question. What do you mean by best. This will be very application dependent. Sometimes a low power MCU is the "best", in other cases clock speed is more important than low power.