The only benefits of aluminum over steel are the weight saving and the polished appearance.
Steel will always be stronger and perform a bullbars function (frontal protection) better.
A winch carrier only is an option but I think they look silly.
Most alluminum bullbars that house a winch will have a steel winch cradle anyway.
ARB and TJM make good steel bullbars.
Also, be carefull on terminology here.... My definitions....
A bullbar is a complete replacement bumper.
A brush guard is a tubular frame contruction that 'wraps' around the factory bumper, grill and headlights.
A nudge bar is a tubular frame that just covers the middle of the factory bumper and/or grill.