For a long time now, we have been using RunCams. And in our opinion, they are the best option out there. Out of the box, you get a Picatinny rail mount - meaning you can put these on almost any gun. And if not, there sure is an adapter available.
Secondly, these Runcams offer multiple Lens lengths. These act as a 'natural zoom', meaning you can get nice distance footage without corrupting image quality. But you can also get a fairly wide 16 mm lens to capture great CQB action.
And lastly, they are simple to control in the field and durable. One button to both turn the camera on and start recording. Priceless when you need to get your airsoft content nice and ready.