It depends on what you like.
This form is for people who like to equal out their attack - since his attack and sp. attack are fairly close. Also, he has great speed.
This form is for people who like to take a step up in their game. His attack greatly increase - this is a good thing since majority of his moves are physical. But, his speed decreases.
Both forms are good! I would prefer the "Therian Form" more, but the sudden decrease in speed is holding me back. So, I think you should choose "Incarnate Form", but not 100% - if you don't care about looks.
Hope I helped! :)