Normally joint/aggregated is the best option for married couples. You would probably be better off on joint/aggregated taxation rather than the other two options of individual assessment (should work out the same as joint/aggregated with any overpayment of tax refunded after the tax year through reclaim process) or assessment as two single people. See this calculator to get an idea of the differences between joint/aggregated assessment and assessment as two single people:
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These Revenue links might also be of interest:
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