All B737's have steel brakes - ******ed if I know why Mr Boeing hasn't offered Carbon brakes but he doesn't
The big problem with the NG - and this causes the "apparent" heavy braking is the high pressure on the brakes required to disconnect the autobrakes.
It is company policy to use autobrake, and before any one gets clever and suggests that we don't use it - just think of the press headlines if the company decided to not use autobrake for pax comfort and there was an incident....
Having said all that, the NG is quite a bit heavier than the classic and takes a fair bit of stopping when heavy..