During the day the 8 & up is busier, night below. ARINC is pretty good about changing bands to maintain good S/N, so unless a feed Rx is in a skip zone the signals are strong if they are in use. The NAT-E coming out of the Azores is pretty good at night, as is the CWP feed. It's really a matter of listening comfort and patience, some of the feeds use higher gain and AGC than is required, IMO, because as I said before, when a band is in use the signals are pretty strong, so listening to hours of high amplitude static between transmissions is not the kind of thing I personally prefer unless contesting.
The new USAF feed has been getting some big spikes in listening traffic, doubtless folks trying to decode the meaning behind the cryptic transmissions and EAM's. To me that is about as interesting as listening to a numbers station, but the equipment he is using is excellent and the quality pretty good.
My own feed, CAR-A 6557/5550, is pretty much manned and tweaked around the clock. I use two R-390's coupled in diversity mode feeding a CV-157 converter, meaning I am always receiving two frequencies at once (the primary and back-up in use at any given time among seven or eight frequencies from 2.887 up to 17.907), so it's pretty much always busy with the Caribbean traffic in the New York FIR.
One easy way to find out current HF frequencies in use over the Atlantic is to tune in the KJFK ARINC VHF 129.9 feed, where aircraft transitioning from ZNY and ZBW high sectors on VHF check in with ARINC to make their initial position reports and receive HF frequency assignments, which occurs at about 250mi out to sea. That VHF feed is also multiplexed into my HF LDOC 6640/8933 feed (along with some other rarely used exotic VHF frequencies) for one-stop listening of frequency assignments, SelCal checks and phone patches.