My quick thoughts based on kit I own and use:
Viper - low quality and would not to rely on it, however, for airsoft it does the job and is very cheap. Have a black tactical vest which although cheap, actually has 6 great pouches that are deep with good sized Velcro flaps that means when playing in the dark I will not loose items from. I also have their adjustable pistol holsters because they are one brand that I can fit my Mk23 into with suppressor attached.
5.11 Tactical - good quality, mid priced trousers and tops, well designed kit that I can use for real world activities and airsoft. Recommended.
Arc'teryx LEAF - very expensive, (professional range) good quality trousers and tops. The Talos trousers actually lack some of the innovation that 5.11 include. For example Talos lack magazine retainers in cargo pocket to keep 2 x 5.56mm magazines in place.
Warrior Assault System - good quality and affordable kit, made for real world use. Wide range of items perfect for airsoft, although they could do with larger pistol pouches and generally longer Velcro flaps to help retention. I am a fan of WAS kit.