Here is the main differences between the three CPU models, this will you a decent starting place to look for a CPU based on your computer use.
Computer processor(CPU) is a part of the computer that interprets and executes instructions. You can think of it as the brain of the computer.
That is, faster processor is better.
Intel has separated CPUs into three performance tiers
|Intel Core i3
|Intel Core i5
|Intel Core i7
|Best fir common tasks like listening to music, email, and Internet.||Smart performance with a speed boost for video, photos, email, and Internet||Best for multimedia creation and serious multitasking|
That is, Core i7 processors will get you better performance overall than Core i5 processors and Core i5 processors will get you better performance overall than Core i3 processors.