There's lot of grinding, but it's doable.
I went for axe as it seems it's the weapon which gives more damage (raw dmg + poison for the best one). Stats full strength, and skills max Axe Mastery and Berserker Hit. Allow 5 to 10 points in Money Collector and Student to help for grinding. Then put 3 points in Sword Mastery and give all the remaining skill points in Natural Armor which gives a nice boost to health. As soon as you can, get the best axe - remember that you can sell the equipped one for 90% of the purchase price. Get vitality equipment when it's challenging. The best vitality item is the ring +10. Otherwise get strength equipment for faster kills.
Hope it helps!
So far, I've tried 2 successful combinations: Death Bringers and 5-8 mines (to clear anti-aircraft units), and Painful Rollers and 2-4 Grunts. For the latter, keep in mind that the goal is to destroy all buildings. Don't bother about air units. Clear first all ground units with the rollers, and finish the buildings with the grunts. Help them outrun the bombers by weakening tall buildings with your shockwaves. Overall a good 4/5 :)
I like the webcomic. But I find this game not very finished.. The laser is way too overpowered. Once you have it you can't lose. Also, the upgrading system is weird: if you buy an upgrade at 10.000, the next one is still at 15.000. If you buy the 15.000 directly, you save 10.000... In other words, just buy the ultimate upgrades each time instead of intermediate ones, and you'll save a lot of credits. Big up for the art and the music though! ^^
The closer you are when killing a spaceship, the more money you get. Max money when you kill it while flying over it. Make sure to buy vertical boost speed early!
 "Legend of Pandora"){kind=icon}
 "Zombotron"){kind=icon}
 "Alienocalypse"){kind=icon}
 "Dragon Age Legends: Remix 01"){kind=icon}
 "The Pocalypse Defense"){kind=icon}
 "Doodle God 2"){kind=icon}
 "Upgrade Complete 2"){kind=icon}