I've generally use shielded cat6, but am looking to switch over to cat6a.

On one job many years ago, even though we ran shielded cat6 to a particular TV, we wound up using an unshielded cat6 for the extender. Lo and behold, the client reported occasional dropouts, which I believe were linked to the HVAC system kicking on. We then switched over to the shielded cat6, and the problem went away.

I know that's just one data point, and we've run extenders over plain cat6 without issue many times, but the story stayed with me.