It seems like the different brands cheap out in different areas, so it depends on what you're working with/for.
For auto, general stuff just about any impact except the really cheap crud from china is going to work 3/4" and smaller.
For me, 3/4" and above 1/2" drive impacts, it has to be Cornwell. It's my experience that they hold up best to heavy use. Do I have science behind that statement? No. Just my experience.
For 3/8 drive impacts I have a lot of Mac stuff and some Armstrong impact swivel sockets that I love!!!
I have never really used the 1/4" impacts, don't know why I thought I'd have a use for them.
If budget is an issue Grey Pneumatic and similar are good bangs for the buck.