The new names of the difficulty levels could cause confusion for some players who have returned to RimWorld after a long time.
Therefore you will find the old and new names of the difficulty compared in this table:
|Strive to survive||Rough||1,0|
|Blood and dust||Savage||1,6|
|Losing is fun||Merciless||2,2|
The difficulty factor is calculated by several multipliers. You can find the exact factors for all the important settings in the RimWorld Wiki.
As you can see from the table, the difficulty Strive to survive (formerly: Rough) is the mode with basically no factor. So this represents the "normal" level of difficulty.
Reload Anytime or Commitment Mode?
In addition to the difficulty level, you can also make a choice for loading savegames. With the Reload Anytime Mode, you can save and load at any time as usual. This allows you to iron out gross mistakes by loading an old savegame.
In Commitment Mode, the game can only be saved if you quit the game. Reloading in the event of a disaster is not possible. This makes the game much more difficult because you have to deal with whatever the storyteller throws at you.
Which level of difficulty is right for you?
Above all, you have to enjoy the game. The Commitment Mode is the originally intended game mode for RimWorld - but if you want to test a higher difficulty level, the Reload Anytime Mode is the way to go.
The best difficulty level for you in RimWorld is the one where you can play in Commitment Mode, while still getting along well with the raids and events. This can of course vary, depending on your experience and your skill.
Personally, I would start with an easy difficulty in Commitment Mode and if it feels too easy, you can always increase the difficulty in the next savegame.