I'd say the level 28. The IV's arent over all much different to the point where the 14 attack will survive to get more moves out, also the level 28 saves a bit of candies.
Though as raids go, for legendaries, theres not many electric is best for, the onlys ones being kyogre, suicune so far. I'd recommend holding off as electric doesnt cover many raids in 1-4, aside from currently azumaril and togetic if it comes back.
EDIT: removal of breakpoint information due to not remembering which match up it was for.