Having gone to a game there in July, I can recommend Frontier Airsoft near Penkridge. Good site, plenty of Marshall cover and a novel and fresh scenario driven day makes things more interesting. 'Capture and mutilate' was an especially nice touch.
I've not been in a year or two now, but Hilton Park (still run by JD Airsoft?)- just at the back of Essington Fruit Farm/Hilton Services off the M6 was always a decent place too.
Several years ago we went to Fireball Squadron near Bassetts Pole monthly for a year or so, and it got too bad for us... Cheating was a massive problem there, and I'm not just talking about players not taking hits...
Having goal-posts un-fairly shifted mid-game by those running the games (not the retired couple who seem to run the site, they were always nice, I'm talking about the guys who ran the games) when Team Fireball were not subject to the same shifts was most annoying. And before anybody says it, no this wasn't about ensuring fluid game-play. It was systemic cheating.
But all players being lectured by one of Team Fireball for not taking hits was the final straw, and here's why...
The guy explained that he opened up an one of the enemy team at maybe 10m distance, but that a dense area of bush and undergrowth deflected/stopped the BB's. However, said the Team Fireball chap '...you know, if real 5.56mm bullets were fired from that close a range, they would have gone through no problem, so, you know, you should play in the spirit and take your hits'...
This to me, is tardation. But even if a site wants to play with such nonsense rules, fair enough, just make it known at the outset that BB's are actually imaginary bullets and if a player deems the real world equivalent to their RIF would have hit you, you're thus dead. 90% of all airsoft 'hard-cover' isn't strong enough to support a fat-chap leaning against it, let alone stop real bullets ffs. But anyway. It just made my lot never want to go their again.
In fairness, that was some years ago now, and things may well have changed. But, there's my thoughts for you.