I use the Milwaukee HD18HIWF daily at work and it's great, it doesn't struggle to undo any wheels bolts or suspension bolts unless they are severely rusted in. milwaukee offer a 1 year warranty on their tools but you can register it for free online to get 3 years warranty, it also only costed me £300. It has been back to warranty once in the first year I've owned it but they picked it up on the Monday and I had it back on the Thursday so it was a quick turnaround
A couple of the lads at work have snap on's latest gun which is a bit more powerful than my Milwaukee but costs £750ish, they only offer a 1 year warranty on the battery tools but after this they only charge around £60-£70 for a rebuild
Milwaukee also do one which is up to 950Nm which costs around £650-700 but you will find yourself stripping threads more often using this one lol
Some more too look at is dewalt/mac tools and ingersoll rand , I know they make half decent impact wrenches but I haven't had much to do with them so no idea on price or warranty etc