For plants?
draw. two. cards. (ill get there in a minute) :D I don´t think there is much thats up to par on turn one even amongst the superpowers.
maybe a well places solar flare or nightcap superpower. the other superpowers are hardly good played turn one or straightup not playable on turn one. I /GUESS/ you can make some great plays with calling in a wallnut and draw a card but beside these?.....Each of them are very conditional and hardly match simply drawing two cards.
Regardless. overall I am rooting for draw to cards. the value is just insane and....cmon. its turn 1. what the worst that can happen (see the lists above)
Why this doesn´t apply to zombies?
Forget me nut/clique peas sure are problems you cannot ignore or that deny you playing powers entirely turn 1.
Zombies sort of lack such potent pro-active one drops so I guess they should rather play a card and start developing the board and spare the draw for later in some situations. Zombies also have much better card draw anyway so its probably fine to skip the opportunity to draw two turn 1 and do something else.
So for Zombies (from playing against them and beeing a salty *)
I honestly thinkg leperchaun is the most potent one-drop in the game. I am not aware of any counterplay and/or any good trades you can make turn 1 if your opponent zombie player drops a chaun.