Ah, Grasshopper, you have stumbled upon one of the basic bones of contention amongst cyclists -- the "Which Tire Is Fastest" conundrum!!! Be VERY, very careful when you open this can of worms...
In my couple of years of Randonneuring (a French word, meaning "Insane Miles"), basically, I'd have to say that changing road surface conditions FAR outweigh effects of particular tire comparisons. Going from smooth pavement to fresh "chipseal" and back will result in a speed change of several (2-4) mph alone.
I'm not sure myself where to find "official" rolling resistance figures, but the "conventional wisdom" is thus:
* Wider, somewhat lower pressure tires roll better over rough surfaces than high pressure skinny ones; For fastest riding, most people prefer skinny, high pressure tires, but they pay for it on rough surfaces through a rougher ride.
* Sidewall flex is a contributor -- a stiff sidewall creates more rolling resistance;
* Tread also creates rolling resistance, and tread isn't really needed on a bike for road riding, since you cannot get a bike up to hydroplaning speeds -- especially since the contact patch to the road is oblong. So go with "slicks"... (What's a "City" tire?)
* Rotational inertia also comes into play, especially in racing where acceleration counts.
* Spokes also contribute to aerodynamic resistance, which is why people utilize disk wheel covers.
Ultimately, for a "Utility" vehicle, include a Kevlar belt or some sort of "puncture proofing" in your tires, whatever you pick. Because flats happen, usually at the most inconvenient time -- and getting a wheel off of a loaded trike creates its own issues.
Ah, mechanical engineering... those were the days...