I was recently in a similar situation selecting 3 PhD students and some Hiwis for a longer funded project. The answer depends in my opinion on what your goals are concerning a distinct research project and how risk-averse you are.
Having a good team atmosphere is of course fine and nice to work in. But I would not make it the primary criterion in academia. Critical and autonomous thinkers are often a bit edgy and individualists. And good scientific ideas (for projects or funding proposals) or a PhD thesis with outstanding results are often the product of such a mind and giving him time and opportunity to work autonomously. In the best case such guys are also team players if several research questions/topics in your group are interdependent (e.g. funded project), but in my experience they often focus more on their thing and ideas and don't want to have to follow a daily/weekly group plan what they have to do.
If you simply have to fulfill distinct interdependent work packages and is it already outlined what has to be done scientifically (method, object etc.), hiring a team player and specialist is probably the much more efficient and wiser choice. But as a subgroup leader seeking tenure you probably not only have a eye on the project/job getting done, but also working on some more difficult/risky ideas with great potential.
So in my case I rather looked for a good mixture of personalities (very disciplined, creative, critical, lab/computer guy...) as there is no perfect PhD student having all abilities/interest/personal traits). It's not the perfect team to fulfill the project, because I wanted to have people with overall interdisciplinary background for interesting side-projects. This means we all have to work a bit more instead of hiring specialist guys matching exactly the projects tasks. But I chose this risk and hope to be rewarded with more research options/results besides the project.
Next issue with assessment is, do you want to hire them only for PhD/project or do you want in best case someone who will stay as a postdoc 1-2 years for different reasons (knowledge transfer, efficiency...)
When you know what personalities you want to have and need, ask the according questions openly and directly to the candidates. I don't think it is efficient trying to be a hobby psychologist here, the candidates are adults and should know if they want and can fulfill such a task over several years and will only accept a very team-dependent, discipline requiring position or a rather tricky topic forcing them to work pretty much alone. The question is more to rule out guys here who just seek a job/salary, but are not really motivated.
If the person is qualified/motivated/knowledgeable to actually do the job is anyway your personal judgement as expert in your area.