I think before you get a recommendation, we should discuss what it means to be a good starter kit. I hate mealy mouthed "it depends" answers, but in this case the context seems especially relevant.
In one sense, the starter kit represents a lot of work in front of you: you still have to learn how it all fits together and works, how it might be modified and so forth.
It is likely that you will do better if you are familiar with the framework so I am surprised to hear that the language doesn't matter.
Finally, you want it to embody best practices so that when you do learn it, you can be assured you're learning about the best security, performance and other standards.
So the recommendation should be: this is the best, if you know Rails, this is the best if you know Django, and so on.
The best starter kit is almost an example app that you can copy, so the closer the example is to the final app you have in mind, the less you have to modify it off the bat and the longer you will have to learn it.
In one sense, the starter kit represents a lot of work in front of you: you still have to learn how it all fits together and works, how it might be modified and so forth.
It is likely that you will do better if you are familiar with the framework so I am surprised to hear that the language doesn't matter.
Finally, you want it to embody best practices so that when you do learn it, you can be assured you're learning about the best security, performance and other standards.
So the recommendation should be: this is the best, if you know Rails, this is the best if you know Django, and so on.
The best starter kit is almost an example app that you can copy, so the closer the example is to the final app you have in mind, the less you have to modify it off the bat and the longer you will have to learn it.