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Your choice between the two should likely mostly be based on what you're doing at that particular moment. If you're looking for some sort of really common / standard form of input (a yes/no/continue/cancel type question for example, or a popup notification of some sort) then QDialog may be less work, but if you're going for custom input, a complex form, or anything outside QDialog's typical capabilities, then customizing a QWidget may be less work than forcing a more complex QDialog.