Lol, I managed to get C survival skills and A+ compassion. I helped everyone but made the worst possible choices that would still have me survive by luck rather than judgement.
I got the best I think survival A, and compassion A+. I didn't volunteer to be bait, and suggested we run past the zombies, I also barricaded the house and killed the infected in the house, only things I did differently.
6836 meters, I'm fairly dizzy now, but a lot of fun, I only played 1-3 times today. I'm hoping to get to 10k sometime and see what happens. For all I know there is a secret cow level. :)
I think level is what matters most for difficulty of being attacked. Massive waves are more difficult, territoriality probably damage matters. Just be sure you have 100k+ before advancing to lv.5, since lv.4 massive wave is the very first tank. The only way to level up is by doing missions, so let your natural income carry you if the game is too difficult. Don't over level.
Lv.10 has more difficult double cannoned tanks coming at you. Seems level is what determines the level of attackers. Therefore, try not to do too many missions and stay low level.
I still dont know what causes the number and difficulty of attackers, your level, how many times the notoriety bar has been filled? I do know that stealing lots of cash, buying a better base, better weapons, #2 henchmen, etc works betters than stealing lots of science too often.
Game only is difficult in the middle, when you might still have first base, basic weapons, and no no.2 henchmen. Once I got the 70 minion max castle the main problem was lag.
 "Frugal Knight"){kind=icon}
 "Ghost! a shipwreck"){kind=icon}
 "Aliens Kidnapped Betty"){kind=icon}
 "Dead Frontier: Outbreak 2"){kind=icon}
 "Dead Frontier: Outbreak"){kind=icon}
 "Dead Frontier Night Three"){kind=icon}
 "Flagstaff: Chapter Two"){kind=icon}
 "Another Cave Runner"){kind=icon}
 "Run 2"){kind=icon}
 "SAS Zombie Assault TD"){kind=icon}
 "Mastermind: World Conquerer"){kind=icon}
 "When The Plague Came"){kind=icon}