[noggin]

Both? There are three :
DolbyVision
HDR-10
HLG

DolbyVision and HDR-10 are both PQ-based and used for drama and movies. HLG is based on Log Gamma and is the most likely to be used by broadcasters (both for live and catch-up/on-demand)

I personally don't think broadcast HDR will be a "thing" in the U.S. for the next several years. ATSC 3.0 hasn't been finalized yet and even when finalized the deployment will take time. What all this means is, by the time HDR becomes a "thing", it will be time to get yourself a new TV.

Here in the UK it's likely that satellite and IP broadcasters will use HDR first, though the main broadcasters like the BBC may also provide content via catch-up - as the BBC are trialling with Planet Earth on the BBC iPlayer.

AIUI HLG is looking to be used here as it requires a single grade and a single deliverable - so is a more cost-effective solution?

On a lighter note, HLG is not "Made in America". Our new President may have a problem if ATSC 3.0 adopts HLG because we have 3.33 HDR formats that are "Made in America"

True... However one of those isn't suitable for broadcast TV is it? You can't do live sport with Dolby Vision AIUI?