I say that execution is more important than the premise/idea, but they're both important. Usually more so than what color panties the heroine is wearing at least.
I treat the concept as the foundation of the show, and the execution as a multiplier for bringing out its potential. Which means if you have a great idea, a great execution will make it a great^2 show. On the other hand, if you have a great concept but a terrible execution, the show will be terrible^2 (screwing up an elaborate idea is worse than screwing up a simple idea). But of course, if you have a terrible story but great execution, the show will at least be watchable. Let's not talk about terrible stories with terrible execution.
They're inherently linked to each other. However, from my experience good execution can save a bad concept while the converse is not true. That's why execution > concept for me.
PS: The analogy continues when you have a great idea multiplied by zero (no) execution resulting in literally no show. Math!