In my company we feel comfortable with
But I'm not sure which of the three, JSS is a "best fit" for, or which will be most supported in the future. Will any of them be a better option, in the long run?
The goal is to support all three frameworks equally, so that implementers can make the choice of framework to use based on the needs of the project and team preference. As of tech preview 4, all frameworks have feature parity as Rich mentioned in his answer.
For a team that truly has no preference, the React ecosystem and developer base is the largest of the three supported frameworks. Until next week, anyway :)
Note: I am on the JSS team.
I don't think you are going to get a fully complete answer here, unless someone from Sitecore can give you some inside information.
But, having said that. If you look at the documentation site for JSS: https://jss.sitecore.net/ - JSS currently has client SDK's for React, Angular & VUE. All 3 have feature parity AFAIK and from Technical Preview 4 these are now considered API Stable, so there are no planned breaking changes.
JSS was original conceived with ReactJS, but the plan was always to support multiple JS frameworks. All 3 are "best fit" for JSS.
As for which you should use/which will be better in the long run? That is up to you. What do you have the most experience with or which skill set does your company have the best resource for? The answer is always going to be "it depends"