This was my report of Mayhem from April this year:
"On arriving, I couldn't find anyone to check in with; three of us eventually found someone in the shop/office. While everyone was prepping their kit, there was a fair amount of dry firing in the safe zone, which didn't seem to worry the staff.
The real disappointment was the games. Mayhem is very much a paintball site, with a number of different fields that could provide some interesting gameplay. However, the four games that we played in the morning all involved the teams starting on opposite sides of a field and having to do something (move a flag, capture a flag, capture a jerrycan) that was a mechanism to bring the teams into contact. This ended up with two lines of players shooting at each other; there was no real possibility to be sneaky or to try something creative. I found it rather boring.
If you are considering going, be aware that they do not do hot food. There are vending machines for fizzy drinks, chocolate and crisps and a tea/coffee dispenser, all of which take contactless payments.
One positive element is that, despite what it states on their website, they chrono on the weight of BB that you are using."
Airsoft Plantation is a site that I really like; it is well run and the games work well.
Splatoon is usually a good day, although there tends to be a little too much time spent hanging around.
Apocalypse is very popular and gets some very positive reviews; I find the marshalling to be poor.
Skirmish Billericay seems to have a reasonably large and loyal fan base; I found it rather disappointing due to some of the game modes (30 people crammed into one small building).
Try a range of sites and see which ones suit you.