Well here are the pros and cons of Nidoqueen DF.
Pros:
It's metal, so of course you know what metal does!
And the power is infinite use.
Attack is boostable.
Cons:
100 HP is bad for stage 2 Pokemon.
It IS metal, so battle frontier kills it's power.
It's attack require more tech.
Meganium DF well... is on my opinion, better because of the facts :
Instant 3 pokemons at the time you play it.
Battle Frontier does not kill it's power.
You can put Energy Root on it to make it harder to kill.
It can find it's own Energy [Holon Pokemon's ; Holon's Castform, Holon's Magnemite etc.]
It has a Resistance to water.
It's Delta Reduction attack is VERY useful [Fact : Delta reduction also reduce damage of snipes to your bench]
It's single resistance can be handled by Holon Legacy [Of course only if you don't need to use Meganium DF's power, you put it down.]
So...? What do you guys think?