[dirtyjim]

I've been using 1/4" impacts since they first came out 20 or so years ago and the 18 and 20 volt ones are plenty strong. as far as 1/4 or 3/8 goes the 1/4 is more versatile around the house but the 3/8 are better if its only going to see automotive use.
the 1/4 adaptors are strong enough if you buy name brand.
I've had just about every brand there is and dewalt and Makita have been the best as far as speed and torque