they all give the same exp, you can check by sweeping them.
the person might be referring to exp reward from quests the ask you to clear a specific instance.

also just a suggestion, exp is not the key point of the game,
what you want is to have a high power and low level

because if your power is low, level doesn't really mean anything, it's totally superficial,
how awkward would it be to be beaten by players 10 lvls lower than you yet still have a higher power?
especially when servers merge in the future, events like the sage war will sort players by power, so people tend to not want to level to maximize their advantage in war.