Best Tactical: Flashbang/Concussion or Stim?

I've been running Flashbangs as they've been useful to throw around a corner and see if I get a hit marker, to know somebody's there, instead of just running in blind and getting killed. I probably use flashbangs mainly for that reason, but obviously the flash effect itself is great too.

On the other hand I could see Stims being extremely useful at certain times, and according to a lot of sites I've been on, the Stims seem to be ranked the highest in terms of best tactical equipment.

Which do you guys prefer, and which do you feel is more beneficial in the vast majority of games? If flashbangs, is there a meta preference over flashbangs & concussions?