Well that depends on the size of your case or luggage. It is very hard to give a one fit solution for all as each travellers needs are different. Besides each manufacturer offers luggage in different sizes. The following is one solution for the most common suitcase sizes. Actually it is like playing Tetris - you can have several combinations of sizes that can fit inside the same case.
2 X-Small, 1 Small, 1 Medium or 2 Slim-Medium
1 Large, 2 Medium (or 4 Slim-Medium), 1 Small, 1 X-Small
2 Large, 2 Medium ( or 4 Slim-Medium), 2 Small, 2 X-Small