Which spell should I use?

[PsychoMagnataur]

a. Shoots a whirlwind outwards, dealing damage in a line. Also spawns several lesser whirlwinds at the targeted area which deal lesser damage.
(Shockwave + Non-Channel Unit-Harming Tornado)

b. Summons several whirlwinds at the caster and shoots them outward. They will pass near the targeted area but not always on it exactly.
(Diablo 2 Twister Druid Ability)

And what should the Druid's ultimate ability be? He has Cyclone Slash (above), Raven Swarm, Elemental Armor (Spell Shield Passive) and Wilderness Lore (Intelligence Attribute Bonus).

I thought of having a transform, into a really strong bear, or summoning a bear, or a mass damage spell.

 

[leissaK]

You can try shockwave for the first one, then make a trigger for a dummy unit walk from the caster to the spot you targeted and make him cast a modified Locust Swarm (with tornado models).

It's too late for me to make the whole code for you, but it should be pretty simple.

 

[Drain Pipe]

I think the dsecond one would be more visually appealing. Maybe it's just me, but whenever there's a skill where you can barage your enemy, i';d take that over just sending out a small ripple. (i'm comparing shcokwave to stampede of course as an example.)