Firstly, individuals need to be selected that are the best fit for roles within the scope of the project. Individuals who possess the knowledge and have unique backgrounds (diversity!) will be heavily sought out. From there, I would consider a Gallup-style test that considers personality. Result-driven individuals, for example, will be strongly considered. I’ll also keep the number of hires to a small number. Smaller teams generally run more efficiently.
As for knowledge vs compatibility – definitely compatibility.

Knowledge can be acquired through experience on the job. A personality that does not mesh with others can certainly hinder workflow even if the individual is knowledgeable.