Forge is the best dude. U can only b hit a few times and then b put in too weak mode. Meaning no one can hit you. And if your being constantly hit u can quest to keep yourself too weak and alsoby being out of troops and spies no one can strip raid you. With defense you can b hit all day while you have money out. But if your worried about being hit then never have cash out which would eliminate the need for any tower or forge.
Don't leave money out then. If you want to leave money out reguardless, I would recommend 1 forge. Then maybe defence towers if you want the extra protection.
4 defence towers is plenty. Even 3 defense towers is enough if you throw in a forge too. You won't get attacked much but the forge is for those "just in case" moments.
If u want. But I say replace everything with guilds and nvr leave money out. That would b ur protection. And do not buy allies. Sell all the ones you have