i'm loving my Snap on 7850, i wouldn't be without it now. I had looked into the Milwaukee M18, it was advertised as the most powerful 18v impact gun in the world at 610nm, I even emailed them to query this as Snap on's 7850 is 949nm!!!!
I never got a reply
Damn. That's serious!
What are some good cordless impact guns? Milwaukee rings a bell.
The milwaukee m18 an snap on 7850 both put out 450 ft lbs of torque, ive used them both an like the milwaukee better plus its alot cheaper
What are you going to be using it for?
Do you want to use the batteries for other tools?

I have a dewalt 12 volt 3/8 and a snap on 14.4 3/8.
I generally grab the dewalt first because it is lighter and gets the job done. The snap on has a little more power but is heavy. I've threatened to ditch the snappy but it's hard to because I spent so much$$$ on it. If I were to buy one today it would have a lithium battery for sure and I'd probably lean towards thew new milwuakees.
Also it's going to depend on what kind of work you do. I work on small engine and primarly work in 3/8 or 1/4 drive.