With different finishes and different sized handle roses, it can get a bit confusing ! Use the handy guide below to determine which size you require.
NOTE: The rose is the round plate which sits behind the lever

NEW DOORS (NO HOLES DRILLED YET)
You can use any size! It comes down to personal preference. 

EXISTING HOLES DRILLED IN DOORS
If you already have holes drilled in your doors and are looking to use these same holes, there are generally 2 size rages: