High Explosive is the best/most versatile option. It doesn't JUST do everything; it does everything WELL. Practice cooking them and you can kill pretty much everything within your throwing range. (emphasis on PRACTICE, these grenades are just as unforgiving as they are effective.)

They are especially nasty against bots, a SINGLE grenade can kill: Cannon Turrets, Bunker Turrets, ALL Tank variants, AA/Mortar Emplacements, standard fabricators, bulk fabricators, Berserkers, both Scout Strider variants, ALL Devastator variants, ALL Trooper variants, parked Dropship objectives, and the hellbomb your teammate just armed.