curves allows more precise adjustments to the pic. levels is simpler but not as precise. up to u to play around n see what u prefer to use. i use curves when i want to be more precise and levels when i cannot be bothered. lol.
Levels give you an easier view of histogram. If you just want to adjust white point and black point, levels would be easier. This is usually sufficient for most photos, alone with mid point adjustment. Curves give you more finer control over the whole range by letting you define individually the way sub regions of the tonal curve behave.