I'd go for the 3/8" one. It's easy to use adaptors to fit smaller sized tool bits on the end, and unlike with cars clearance is very rarely an issue when working on bikes.
@Brommers started
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I'd go for the 3/8" one. It's easy to use adaptors to fit smaller sized tool bits on the end, and unlike with cars clearance is very rarely an issue when working on bikes.