I'll say Blackstone CQB for the reasons mentioned above. It also has vending machines along with free tea & coffee plus the fact that the setup area/safe zone includes the White Sphere shop and a 20m shooting range.
In addition to CCTV, the games are streamed on Twitch with a slight time delay. The play area has also had changes since it opened that have mixed up game play. Hot food may not be sold on site but you have McDonalds, Burger King, Nandos, Greggs, Wendys and a large Tesco store among other places to get food within a 5-minute drive of the site. The site has decent toilets also. As you book and pay in advance (to discourage no-shows when the head count at the site is already low), you just need to confirm you have read the disclaimer so you're not queuing for long at the start.
I would also vouch for UCAP Dover/Vanquish. The Citadel is a good site to play at as you have so much variation of buildings to navigate through when pushing to complete objectives. When the weather's nice, you get a stunning view of the Dover Strait from the south of the site and from the car park. They only make food to order so you need to get your order in early as you won't be able to decide you want something hot during the lunch break. You just have to bear in mind that they don't allow two-tone and if you have smoke pyro that has any red colour base to it, you can't use it for the risk of mistakenly alerting the coastguard. Considering the nature of the Citadel having been a detention centre, prison, borstal, barracks and other things, you'd think it would have a decent setup area and it does. The entrance to the setup area is a little clumsy though as walk-on players get in the way first thing in the morning.
COMS-3 near Chipping Warden was a brilliant site and I'm confident it will still be when it is expected to reopen by this time next year. The site has a bunker, trenches and lots of areas to attack from or defend. The site is going to change a little bit because of some land loss caused by HS2 but new land will see new features being added. It will have the same marshals at Blackstone being rotated so you will be fairly treated.