The sniper has a less health but they have a really high damage output. You can usually take care of anyone other than a tank in one shot. Not to mention the increased range so you can shoot them before they even see you.
I absolutely love the car. It's wonderful. Your practically invincible with 3x the speed and you can run over anything....except that kid on the mountain....I tried killing that kid (cuz I'm messed up that way, mind your own business) and nothing would work. Bullets and cars. That kid has the power to stop a speeding car XD!! ....Anyway, I played with the car and I was rolling uncontrollably and got stuck on a tree. Like, it was leaning on the tree and I couldn't move it at all. Also, there should be a way to make up for killing an entire village because you can't finish the quests and that turret starts to hate you. (Maybe stuff them in a car and take them to a hospital?) I also found that a car can climb a vertical cliff if theres momentum. An absolutely lovely game. I hope you complete this soon.
I have found that if weak enemies are spawning continuously, then missiles will rally up together and turn into a giant concentrated missile ball of doom.