who's the best dps hero, apart from jaques (which I already have)?
trying to pick a hero to buy next

Mako

Try new guy Fenris, he's wise-choice-target hero (although sometimes he is stuck when running to his target)

Many players use Mako as substitute for Jacques, especially in Abyss where Jacques and Rose are banned.
So do not forget about Rose - she is banned with good reason. She is very high damage dealer!
Main difference between Jacques and Rose is that Jacques does higher damage at start of a battle (good for dwarfs or time trials) and Rose is increasing her damage over time (good for Lich and duels).

Another high damage dealer is Vallari. Maybe even higher then Mako. Only difference is that Mako is doing focused damage on one target (good for dragons in Abyss) and Vallari is attacking multiple targets at once. But i have seen reports with level 50 Vallari doing 5 or more millions of damage.

think I might go for fenris. waiting for fenris set to come up in shop...

Personally i would go after Jacques/Elena/Cleo/Rose first, then race specific heroes with passive skills (depending of your race, but late game you actually play all races). Right now i see Fenris specifically designed for Abyss. Which is OK if you have all the heroes and you want to finish those +320 Abyss levels. His main advantage is his versality, where he can be a tank unit or a commander (depending of distribution of his skills)