I went with the 1/2" impact and use adapters for 3/8" sockets when needed. I'd imagine 1/4" would be quite weak.
Go for the 1/2" or 3/8"...1/4" is tiny (you want an impact wrench, not a drill).
I bought mine almost 2 years ago (Harbor Freight, Chicago Electric, corded) and use it all the time. The cord is not inconvenient and it beats hassling with dead batteries.
Only use impact wrenches for loosening, not tightening, or you'll snap bolts.
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