Trying to read the question correctly...initially thought it was "If you could only have one kilt and that's it forever." (what an agonizing question)...

Would probably be a Utilikilt so I could get the most wear out of that one kilt.

On the other hand sounds like maybe the deeper question was, "What's a good starter kilt?"

That question doesn't much matter, since there will be more kilts once kilted.

Ron