Panel data - first differences model

I am using panel data (world bank's world development indicators). Need to create a first differences model. Not sure whether to use reg or xtreg....i.e.

Code:

reg d.y d.x1 d.x2 i.year, vce(cluster country)

or

Code:

xtreg d.y d.x1 d.x2 i.year, vce(cluster country)

Any word on this?

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