I use steel for one simple reason - I am not opposed to replacing parts when they become damaged, and steel bars in my experience perform well at protecting delicate components up front of the vehicle.
When I lived on the mainland, the times and routes I travelled unfortunately meant that animal strikes were part of the game. What I have found with steel is that it protects vital components (eg intercooler, radiator etc) well because it doesn't deform much (or mostly, at all) on reasonable sized hits.
On some larger hits, I have seem vehicles where the steel bar is heavily damaged - but the vehicle is driveable. A friend of a friend had a smart bar on his Pajero, and after one particular incident with a hairy grasshopper, the bar looked perfect. Unfortunately it had flexed so much when absorbing the energy of the impact that the radiator was fractured rendering the vehicle un-driveable. Sort of defeated the purpose of having a bar fitted...
Admittedly that is my only direct experience with smart bars.
That being said, I can see how they would be appealing to people for a variety of reasons. Comparatively light weight, comparatively pedestrian friendly being among them.
As everyones needs are different, a smart bar might suit yours perfectly well and would be a wise choice.
For my needs - the bars primary purpose is to protect the front of the vehicle in an attempt to keep it driveable in the event of an animal strike. Anything else is secondary. As such, the only one that fir MY needs was steel.
My recommendation would be think about what you want from a bar. Make a list, and rank it in order of priority and likelihood of event happening. Go from there.