It depends on the steak.
If it's a good cut, well seasoned, and cooked just right - I don't need steak sauce.
If it's just your run of the mill sirloin from the grocery slapped on a grill until it's brown on both sides, I tend to cover it in A-1. That said, I'll find excuses to eat A-1 because I love the stuff... Put it on bread, etc.
Yes, I'm strange.
This is funny to me, because my daughter will put it on her popcorn.
I also use it depending on the steak and how well it is seasoned/cooked.