Which Pokémon should I power up?

none of these are worth powering up, you will find way better pokemon as these arent that strong. Save your stardust until you get to a higher lvl and get higher tier pokemon

Don't bother with the Gengar or Hypno - you're better off evolving higher cp'd starters. I like Seadra's but they're not really useful for anything but training gyms. The Golduck will make a decent attacker if you've got lots of stardust, but he'll never be as good as Vaperon. The vileplume's moveset doesn't really warrant upgrading, but he's useable as is.

Don't bother with the Gengar or Hypno - you're better off evolving higher cp'd starters. I like Seadra's but they're not really useful for anything but training gyms. The Golduck will make a decent attacker if you've got lots of stardust, but he'll never be as good as Vaperon. The vileplume's moveset doesn't really warrant upgrading, but he's useable as is.

Golduck would make a solid attacker. If you really want to power up some of these, only golduck worth it.

Break the vaporeon meta!

Dont waste your stardust with these bad pokemons.

Any of them you like. Seems like you could catch a much much high cp gengar/hypno during event though. Enjoy your game.

I'd say don't waste stardust on any of these. Two main reasons:

1. With the exception of Vileplume (and, some people might say, Golduck), these are all lower tier attackers/defenders. Why invest dust into them when you could power up Dragonite, Lapras, Snorlax, Arcanine, Exeggutor, Vaporeon, etc.?
2. The CP on all of these is pretty low - you'll catch much higher level pokemon as you level up as a trainer. Even if you want to use something like a Hypno, why invest dust in a 283 CP mon when you can catch 600-700 CP Drowzees in the wild later, yielding a ~1600-1700 CP Hypno for no stardust at all?