Executor doesn't let you pray unless you unequip it. Could be a nasty surprise at some point. But I guess that's beside the point...
Objectively, Executor is better - it kills faster, in some cases a lot faster (non-humanoid demons). Level 4 and level 7 - that's nothing. You're at level 7 from scratch in, what, about ten minutes play time? Difference in actual stats? Couple of points in to-hit and damage. That's nothing either.
Anyway, both of these weapons are endgame worthy. Use what you think is more fun. Use both if you feel like it.
Also: Prepare for the twin daggers? By the time you've got them, you're basically done with the game. You don't need to "prepare" for them. They don't matter. Serpent's Bite, alone, has ten times the value, meaningfulness and usefulness of Needle and Sting taken together. It slays humanoids and poisons the shit out of your enemies, all the way down to D:50, and you can get it in a lesser jelly vault on D:12. Or one of these 200 stomafillia precrowning romps people seem to love doing so much. Executor, same deal. Both are awesome.
Which do you choose? Who cares? You've got a whole parade of much bigger problems this early in the game. Having both Executor and Serpent's Bite, in fact, is not even a problem, it's the very absence of a problem. Focus on everything else (except your shield, because that one rocks your socks off too). Focus on getting some more spells, focus on boosting your Toughness and so on, and most importantly, focus on not getting your ass killed!