I would do Kael first for simple reason clan boss and dragon   

The main job of your first level 60 is campaign farming. Seems like Trunda should be able to do that, with good enough gear. She's definitely much better than Kael in arena and she's more of a long term investment than he is. But definitely, Kael is more versatile due to his poison. 

Another factor is, are you going to skip taking Kael to 60 entirely? Do you already have other champions who can fill the poison role as well or better, so you could take them to 60 next? 

If you do plan to use them both at level 60, it probably makes more sense to start with Kael. But if you figure you don't really need Kael at all, then indeed you could skip him and avoid spending a lot of effort on a champion that you'll stop using by the late mid-game or end-game. 

Raid said:

Would it be nuts to take Trunda Giltmallet to 6* before Kael?

This will be my first 6*. I pulled Trunda early and I've really enjoyed playing her. That said I don't know if Kael brings more to the table and should be my first 6-star.

Please give me your thoughts.

One of the best ways to learn this game is doing something crazy.  If it works you learned and are a genius.  If it fails, its back to the drawing board. 

To answer your question, Kael was my first quality hero.  I took him to 6* with masteries and books.  I never regretted it. 

Do whatever you want, nothing change in the end.

If you are new Kael would be better. He would help you farming to Brutal, from then you will use him forever. 

Do whatever you want, nothing change in the end.

If you are new Kael would be better. He would help you farming to Brutal, from then you will use him forever. 

Kael will become obsolete. Trunda will not. That said you will probably 60 both.