Attached here is a third-party guide that displays how much EXP each individual level gives (https://axieedge.com/adventure-mode-pve-exp-leveling-guide/).
Each level gives more EXP than the last one, and thus, it is rather obvious that players should keep on repeating the highest level they can clear if they are trying to farm EXP and not SLP.
However, what if you fail to clear it? Well, that's when players are recommended to decrease their level by one and keep doing so until they level up. Then only should they challenge the next level.
Players should not spend too much time on Adventure Mode and should be able to pass each level by simply playing all their cards each turn.
Otherwise, it will take a long time to farm 100 SLP daily.