I know that I've been putting this as an answers a lot lately, but I think a Diplomat would be good here. In this case, for defense.
I know that the city could be a target, and I actually think that a diplomat would be BETTER for defense than a pike. If two crusaders land, we may not be able to defend ourselves properly and would have to rush a crusader or something - all the while dealing with an attack that could kill units and lower population. With a diplomat, we could bribe a crusader and have it attack the other attacker. A quicker and easier solution.
Plus, the diplomat doesn't need any support - which will be nice if we switch government. Then, when the phalanx and archer upgrade to musketeers, we can send the dip out on the offense!
My vote, therefore, is for "other".