The best gun is the railgun. you can find it when you clear one of the "crash" sites in the map. it costs 800, but a headshot can instantly kill anything and it has obscene range. get that and the sniper, get a lot of bullets, and you can take on anything :)
+ this comment!
 "Bongo Boom Battlegrounds"){kind=icon}
 "alien exterminator"){kind=icon}