Before.
A good simple marinade is olive oil, black pepper and salt.
I remember there was a some PSA on TV back in the seventies about food safety, and it advised that you salt meat after cooking, because supposedly salting it before dried the meat out. Maybe that’s where people got the idea from.
I think it is imperative that one give the steak a coating of oil and a heavy seasoning before grilling to keep it from drying out. It has been explained to me that the coating of oil isn’t to keep it from sticking to the pan/grill, rather it is to more efficiently transfer heat directly to the steak and give it a proper char-crust. I think the seasonings really add something to the steak flavorwise as well, if not acting chemically to enhance the caramelization and sealing of the meat.
My method:
Remove steak from fridge. Open package so meat can start becoming room temperature. Sprinkle generous pinch of Kosher salt and fresh ground tri-color pepper on the side-up. Wait 30 minutes. Heat skillet screaming hot, put steak in seasoned side down (nothing added to skillet). Sprinkle naked side of steak with small pinch of Kosher salt and pepper. Timer for 4 min. Steak starts to smoke a little. Flip. Turn heat down to medium. Timer for 3 min.
Delicious crustiness on both sides, medium rare, perfect every time.
Now I’m hungry.
Yeah, I do mine naked in the pan as well, but for thick steaks I do it this way: salt & pepper, put in 275 oven for 20 minutes (straight from the fridge. If you’ve brought them to room temp, you can cut the time. You’re shooting for an internal temp of 95 degrees or so at this point). At last five or so minutes, heat cast iron pan over full heat until white-hot. Remove steaks from oven, 2 minutes a side on the pan, rest a couple minutes, serve. Perfect steaks that are medium rare all the way through except for the 1/8 inch of char on each side. No oil necessary.