Either you farm enough sp in your late 20's
to lvl up 2 nuke trees as soon as you hit lvl 30,
or you go through with lightning for highest speed and damage till lvl 30 and lvl up the 2nd skill tree afterwards.
If you want to do it the "highest damage way",
take
lightning and
fire with armor


pros:
[*]1 hit kills on higher mobs with flame wave

[*]faster lvl up
[still fast with grass walk

contras:
[*]fire skill tree is mainly for the nuke, so you need more sp
you don't really need anything else in the skill tree
[*]more prone to dieing due to lack of physical defence
[*]less speed if you choose armor as your suit.
If you want moderately high damage and better defence,
take
ice and
lightning

Pros:
[*]Slow down mobs with nuke to finish them of with lion shout (2 hit kills no damage)
so almost no hp pot consumption


[*]Still have splash damage with wolfs thunderbolt and be able to survive more mobs attacking with snow shield.


[*]more damage reduction through ice defence skills: better against giants and prty mobs



[*]no extra skill tree only for 1 skill: less sp needed
Contras:
[*]less 1 hit kills than fire
[*]more mp pots needed