First of all, SMN is not like other classes. We are DoT class. I don't understand why people are comparing to other dps classes.
For Solo, it's very easy. Bio II, Miasma, Bio, Fester, Ruin II, Ruin I. Target dead (combined with pet's attack).
In dungeon, Bio II, Miasma, Bio, Miasma II, Virus, Fester (single mob), Bane (multiple mob), Tri-disaster (multiple mob), Shadow Flare (multiple mob) and Ruin II. Throw in Aetherflow, Rouse, Spur and Enkindle somewhere in there too. I also use Thunder cross skill DoT too.
In typical dungeon, there are easy adds, that died before all DoTs finish their course. But 95% of mobs last 2-3 times the length of DoTs. And it's always 2-3 mobs per fight. I don't target one mob, I target all with Bane. When first mob died, second mob is at 85% health from Bane's DoT spread. When second mob died, third mob is already at 65-70% health.