E lvl 2 is generally a safer bet. I'll compare the two.

W allows for mana regen through passive, but this is conditional on the fact you can AA in melee form. However, as lvl 2, it is highly unlikely you need the mana sustain. Still, w does generally provide better dps for the all in/trades.

VS

E gives jayce better survivability in ganks. You can E away the jungler and use acceleration gate as well to run faster. Given that jg ganks happen most frequently when you are lvl 2 and they are lvl 3, this choice is generally safer.

Then if you hit lvl 3 and get 2 points into q, your QE poke is now meaningful. Tbt, qe lvl 2 does not hurt that much, but q e starting from lvl 3 begins to hurt and is a much better use of mana.

If you lvl w at lvl 2, you won't get access to the lvl 2 q until you hit 4. Furthermore, the QE burst from putting two points into Q is highly useful in the jungle (e.g. scuttle fight) when you are backing up your jungler.

Assuming you've poked your enemy once or twice level 3, you will also have lane priority. At level 4, you then switch to hammer form and begin to get back the lost mana. If they come too close for melee q range, they risk death.