Most useful? Most powerful?

Tell me which one you specialize in and perk for and why.

I chose frost for its slow effect. Since damage doesnt scale, and magic resistance is easy, a slow effect for avoiding melee hits worked best for me.

Yes many of the characters are nords and have a resistance to frost. If you want the type with the least natural resistance you will want shock.

I got the damage increasing perks for all 3, but haven't gotten the ones past that yet. Personally, I think Lightning spells are the easiest to hit with since you don't really have to worry with travel time, and they're the most useful against enemy mages due to their inherent magicka damage. Still, I wouldn't rely on any single damage type with Destruction magic, since certain enemies can have high resistance to some elements but a weakness to others.

I think I prefer lightning, they are easier to hit with IMO and they drain mages magicka which is very useful

My only destruction mage so far has gone for cold. Sapping the stamina so they can't do power attacks and slowing their movement speed makes them easy targets. Still I havent progressed that character to higher levels yet. You still kind of need all of them for different situations though. Lightning against mages, and fire against vampires. You can't stick to a single type for every situation.

Very few enemies are resistant/immune to shock spells, but yeah, different spells for different occasions.

It depends

Fire is a general attack that works well on enemies that aren't resistant to it and it does damage over time.

Frost works well on melee opponents, doing damage and draining their stamina.

Shock is very effective against mages, draining their magicka(making them useless and defenseless) and causing them damage,

So really, the magic spell are very situational and if you use good tactics, are very effective.

The shock master spell is very powerful if you have enough magicka (which you won't unless you enchant for 95%-100% destruction reduction), if you have the +shock perks as well.

I tend to mix it up. Frost on warriors, shock on mages and fire on anything I want my companions to kill. Shock works VERY well against Dragon Priests.