Yes. Whenever possible you want one of your thunder spells on the target enemy. As Taika explains, the overall damage of the DoT is much higher then the initial hit would indicate. And at your level you have a trait called Thundercloud. Every 3 seconds when the DoT ticks you have a chance for the trait to proc. When it does, you get a free enhanced cast of either thunder spell. The thundercloud enhancement is instant cast, no mana cost, and it does the full damage of the DoT on the initial hit PLUS applying the normal DoT effect to the enemy. A thunder 3 cast via proc does close to or more damage then a fire 4(it depends on how long the DoT was on before you activated the free cast). When fighting one or two enemies you can individually DoT both of them with T1/3(the single target one you have), when fighting larger groups putting the AoE thunder(2/4) down in the middle of the pack is a fine way to spread the damage. You get the best potency-per-cast return by casting/reapplying your thunder DoT during your ice phase, but remembering to keep it going is almost always a good thing. Quick note: the AoE versions proc the thundercloud trait a lower percentage of the time then the single target ones do, but once you have a free cast you can use it on either version. Hope this helps.