Helicopter Cannons: What are the advantages?

I am interested in your opinions on which turret mounted cannons are best for a CSAR helicopter, ie: Chin turret for the EH-101 CSAR Helicopter.

I am thinking of the RMK-30:

“Recoilless Automatic Cannon RMK 30: The RMK 30 is the first recoilless automatic cannon in the world. High firepower, low mass, compactness, rigid and simple design as well as high operational availability are the main features of the RMK 30. High integration flexibility allows the RMK 30 to be used as combat mission kit on almost any kind of light military vehicle or as main armament for modern infantry fighting vehicles and helicopters”

but there are many more on the market such as the Giat THL 20 and THL 30:

“Giat Industries offers two turrets, THL 20 and THL 30, designed both to be fitted to attack helicopters and upgrade helicopters initially intended for transport or observation. These two turrets are developed around the same architecture and are fully integrated into the helicopter’s weapon system. Slaved via a databus to aiming systems (headset sights, roof-mounted sight), they provide remarkable laying accuracy.

The THL 20 is developed around the 20 M 621 cannon, widely known for its great versatility and firing the NATO-standard 20mm x 102mm ammunition. The THL 20’s highly reduced integration requirements (weight, overall dimensions, recoil force) and its simplicity (operation and maintenance) make it a turreted cannon which is particularly well suited for upgrading existing helicopters.

* The THL 20 is qualified on the IAR 330 helicopter built for the IAR Brasov company (SOCAT program)
* The THL 30 is developed around the 30 M 781 cannon. It fires the NATO-standard 30mm x 113mm ammunition. The 30mm calibre provides the best weight/firepower ratio
* The THL 30 is qualified on the Eurocopter’s TIGRE HAP helicopter”

Plus of course there are the Boeing bushmaster cannons and chain guns, and the XM-301 designed for the commanche.

I have searched google for info on all these weapons, but cant any comparison tables…