The only aggressive shell that would run both is Rakdos, which would prefer
Shock.
This.
I have done a lot of testing with aggressive Rakdos decks (Vamps and Artifacts) and most of the time I would favor having Shock. Keep in mind also that Rakdos also has access to
Unlicensed Disintegration which similarly fills the role of Push (removing stuff regardless of toughness) albeit slower (but with the potential of extra reach as well).
Should you have access to discard outlets as well (which Rakdos likely does) then
Fiery Temper should be considered in the discussion also.
My current Rakdos Artifact build runs 3x
Shock, 3x
Fiery Temper, and 3x
Unlicensed Disintegration and generally doesn't have too many issues where it needs unrestricted removal and doesn't have a UA in hand. Shock and Temper cover most things early on to push damage, and by the time thing start dropping that need that more potent removal, you should either have a UA in hand, or have the opponent close enough to death to burn them out with Shock/Temper/UA in combination with your aggressive (preferably evasive) threats.
Were I to include Push in my deck, the furthest I would go would be -1 Shock, +1 Push, and I still don't think that would be particularly beneficial (since the face burn is so relevant in the deck).
Could you post the deck in question? Would probably help to better understand which is better for you.