I'm in agreement with duke.
Hopefully, as we progress into republic and later democracy, cash will be a pretty decent weapon for us. Dips, and later the all-powerful spies, are great on this type of map for the very reasons duke dictates.
Further, with no support and no happiness issues for being outside of the city, they are very versatile. If we ever needed to steal some tech, bribe an outpost city, set up an embassy, etc - then it'd be nice to have a few available as well.
Finally, I actually think that dips are 10 shields CHEAPER than crusaders. Again, I THINK that's right.