I have serpent queen, angel, pain da, executioner, cyclops, werewolf, assassin, shaman, engineer, and frost witch.
I currently use executioner, pain da, cyclops, werewolf, angel.
I would rather have the shaman than pain-da. Since the shaman is the 3rd highest hp hero in the game (after paladin & werewolf) and is range. Pain-da special doesn't affect air (not sure about buildings) and air units is the norm.
I'd rather have Pain-da
not everyone runs air units (especially in his might range), and I'd rather have his AOE special than Shaman's useless one (and the hp difference is negligible)
Also SQ over Angel
If your engineer is a high enough level i'd bring him instead of both painda and shaman
ranged+better skill, just don't let him be the target of attacks and the hp difference shouldn't matter