1) The best unit to defend yourself is of course the porcupine, due to its extremely low cost! Any other unit worth using to defend your precious factory or base simply requires a significant amount of cash!

2) Concentrating more on factories, than a BASE since if someone is pounding on your base, in most cases it means, dying is a matter of time! The second best unit to defend is the Patriot. One patriot costs 4 porcupines; yes, it can gain valuable experience and can attack as well as retaliating to an attack! You will find that a fully experienced (8 stars) patriot that has full health can be a pain to kill!

3) Third comes the Scorpio together with the Metalknight. They both make one hell of a defense despite their high cost. The only problem is acquiring the university for them, that is probably why I would favor the scorpion a bit more than the Metalknight! A brand new Scorpio can easily become a nuisance in a fortified city, let alone an experienced one! The great advantage given to both is that they can both be then used for attacking purposes too! So they are not going to be useless units, stacked inside your factory! Even when 4/8 units are destroyed, they can still punch hard! Think of them as a double Grizzli!

4) The fourth (or more like 5th) unit to defend your factory, is of course the Captain! At a defense of 13, it poses the same defense as a Metalknight! Its advantage lies in the fact, that if the map has wrecks - which most maps do - you will have this university practically "free"! Only problem is that it is useless in a city and can only serve as a defense measurement, since it cannot attack on land. However, you could always make use of it at sea!

Note: Always fortify your factories! The extra defense they add to your units make up for the additional 30$! A porcupine can sometimes be invincible at 240, whereas it is much easier to crack on the 200 mark!

In cases where the map is extremely poor, there are some other options offered!

Usually the best unit to defend your cities, is still the porcupine, however, the Elf can prove extremely useful too! At a defense of 5 and being discovered almost immediately in the game, when placed in a fortified city, it can withstand anything up to an attack of '6'. It also fights back, so if your opponent attacks you with his own Elfs, chances are he will suffer great loses without even scraping yours! In poor maps, the patriot can also be favored, rather than the porcupine! Its ability to retaliate to any attack makes it valuable, since every unit counts! One patriot may render a handful of enemy units useless, by the time it has been destroyed.