My suspicion is that this is not answerable in general.
To a first approximation: whichever of the two your political leanings make you more comfortable with.
To a second approximation: if your task is efficiency at a constrained task, homogeneity. If your task requires exploration and/or creativity, heterogeneity.
To a third approximation: the 2nd approximation argument, except the demands of nearly all tasks change over time.
Then you factor in the environment, including your management's competence at eliciting the value of various team members, etc.
And don't forget risk. Optimizing for a high level of performance in any dimension makes things brittle in all other dimensions.
To a first approximation: whichever of the two your political leanings make you more comfortable with.
To a second approximation: if your task is efficiency at a constrained task, homogeneity. If your task requires exploration and/or creativity, heterogeneity.
To a third approximation: the 2nd approximation argument, except the demands of nearly all tasks change over time.
Then you factor in the environment, including your management's competence at eliciting the value of various team members, etc.
And don't forget risk. Optimizing for a high level of performance in any dimension makes things brittle in all other dimensions.