[Heironeous]

I like to use a fortified city for Man (standard) in combination with a big blessing for my wardens. Clear out the provinces immediately around the capitol and watch the resources pour in. Note that I usually play on smaller and/or crowded maps, and my choices (Man, fortified city) reflect this.

Yes, build time is a pain, and like Verjigorm said you do need to be very selective when building a new one. I suspect Ulm could make good use of a fortified city (needs lots of resources, has lots of gold) but I've never tried it myself.