Keep this Tangrowth?

Question

After DexNav chaining 20 Tangela, I managed to find a Regenerator one. It came with a Quiet nature, which raises Special Attack and lowers Speed. Originally I wanted a Relaxed nature, which raises Defence and lowers Speed, but I wanted to see if this nature would work with her planned moveset.

Tangrowth@ Leftovers
Trait: Regenerator
Nature: Quiet (Relaxed)
EVs: 252 HP, 232 Def, 24 Atk/24 SpA
- Knock Off
- Giga Drain
- Earthquake
- Sleep Powder

The only move boosted by Quiet would be Giga Drain. Is the slight drop in Defence worth it for the slight raise in Special Attack? This would save me a lot of breeding time. Also, before people start raging "Why you no run HP Ice?" this is for ORAS WiFi singles, so my options are limited. At the moment her Hidden Power is Psychic.

I don't have a solid team of six yet, but I do have a Fire/Water/Grass core with Heatran/Mega Gyarados/Tangrowth. Her teammate's movesets are:

Heatran@ Air Balloon
Trait: Flash Fire
Nature: Modest
EVs: 252 SpA, 244 Spe, 12 HP
- Stealth Rock
- Taunt
- Earth Power
- Lava Plume/Fire Blast

Gyarados@ Gyaradosite
Trait: Intimidate > Mold Breaker
Nature: Adamant
EVs: 252 Atk, 188 SDef, 48 HP, 20 Def
- Waterfall
- Earthquake
- Crunch/Dragon Dance
- Substitute

Answer 1

No, ditch it

Try to get the Bold nature in which that is more preferred. And change EQ to Leech Seed because it is overall better for stalling and that kind of stuff. And you need to change your EVs a bit too. Here is the final set:

Tangrowth@Leftovers
Trait: Regenerator
Bold Nature
EVs: 252 HP, 200 Def, 56 SpD
-Knock Off
-Giga Drain
-Leech Seed
-Sleep Powder

Hope I helped!