The stock Source 1/Half-Life 2 explosions were the best, change my mind.

I mean, they look the most realistic. Military explosives like C4 or Hexotol (which are more prevalent in FPS games, because, you know, demolition charges, rocket launchers and hand grenades) are not meant to produce a large fluffy volumetric fireball you might see in movies. Those are characteristic for gas or combustible dust explosions, which are deflagrations, not detonations.

HL2's explosions, while not being spectacular, are more correct - a couple of sparks, very little flame, a shockwave and clouds of smoke and dust, and that's it.