You will get a wide range of feedback on the two Focal Utopia threads over at HeadFi.org
I went with the DanaCables Lazuli Reference and absolutely love it. My setup of the Schiit Yggdrasil - HeadAmp GS-X MkII paired with the Focal Utopia was slightly bright with some recordings (to my ears and preferences) and I wanted to use all copper in the cable I went with. The Lazuli Ref is pricey but, in my opinion and for my preferences, was a perfect pairing with the Utopias.
That's a long length and will be correspondingly pricey if you go with some of the higher end options.
Even the Kimber Axios, which some Utopia owners are using with good results, is pricey.
Hope that is helpful. Let me know if you have any other questions.
- David.