My two favorites are sardons and swamptown,
Sardons is easy to defend, and the spikes do half the work. Plus, if you use drag view, you can buy bombs and arrows from snowtown.
I like swamptower because, like sardons, I find it easy to defend, and it makes me money ;)
The entrance to flag is easy to defend, and down by water is also easy to defend.
My LEAST favorite is snowtown, the ice makes the pkers faster, and when they're on their horses its even more annoying *___*
The only positive I see to it is blocking the hall door.