I'm going to have to say the better Raiton user of the two is Kakashi.
Kakashi simply has more experience, and I'm pretty sure it's his primary/natural element. Sasuke has ''stronger'' techniques, sure.. the Chidori was ''passed on'' to Sasuke in a manner similar to how the Rasengan was ''passed on'' to Naruto. Just like Naruto built upon the Rasengan, Sasuke built upon the Chidori.
Normally I'd say the previous generation is surpassed by the current one, but in this case I don't think Sasuke has achieved a level of Lightning usage that Kakashi has. Just an opinion, but I believe Sasuke is far more suited for Katon techniques, and will probably be using a lot more Katon/Enton techniques to match with his now undying patriotism and love for a clan that virtually no longer exists.