gun game is one of the worst modes to improve your game. you will never use any weapon besides glock/usp/deagle/mp5/ak/colt/awp. maybe famas/galil, not too sure of CS:S.
So if you play gun game you are spending a huge chunk of time using weapons that will never matter.
Deathmatch is a good way to improve your aim/reaction - plus you will auto-respawn with your colt, ak, or awp. The only way to improve your competitive smarts is with scrims.
(lol @ hostages.. who the fk plays hostage maps
)