Pokémon Moveset and EVs.

Hello guys, I would ask for help. Today I'll ask about Meganium's Moveset and EVs.
In my opinion Meganium hasn't interesting attacks in third generation, however, can you help me to find the answer for this problem?

Meganium's Moveset:

- Ancientpower. It is an Egg Move, it is useful against Fire, Ice, Bug and Flying Pokémon.

- Earthquake. It can be teached by MT and it is useful against Fire, Poison and others Pokémon.

- Body Slam or Double-edge? Which is better? Double-edge is a Tutor Move.

- Solarbeam, Giga Drain or Razor Leaf? Well, the first is the most powerful and i like to see that "120" written in the description, but is counterproductive because the time of waiting. Giga Drain, in my opinion, can be useful with Double-edge (recoil then recovery), but it has only 5 PP. And what about Razor Leaf? Weak but it gives STAB.

So guys, what can I do?

Meganium's EVs:

I thought that a Sassy nature can give an advantage on Special Defence, then I can give 252 EVs to Defense and 252 EVs to Attack... Why Defense and Attack? Well, I thought that Meganium is week against Flying, Bug, Poison, Ice and Fire, but the first three types are Physical and it would have a Rock-type Attack, a Ground-type and a Normal-type, so Attack can be more useful...

What do you think?

Sorry for grammar errors... :(

Please ask in the Competitive Team Questions thread for questions like this. You can also use the In-Game Team Questions thread, but I recommend the former because you're asking for EV spread suggestions which aren't normally bothered with in casual or in-game play.