I use TOPO 24k US Northeast on my Epix and my Edge 1000. (They used to sell the TOPO maps unlocked. That's no longer the case; I believe they're restricted to a single device now.) I use City Nav on a Nuvi and an in dash Honda navigation system.
Advantage of the TOPO maps: topography. On some devices and in BaseCamp you get relief shading to bring out the topography because of the build in digital elevation map. I live in central Pennsylvania, and I want topography. Some trails might be on them; you won't find any trails on City Nav, which are intended for automobile travel.
Advantage of City Nav: assuming you buy the subscription, they're regularly updated. I've never seen any indication that the TOPO maps have been updated since I bought them (six years ago?). The information about POI's included in City Nav is not always accurate, and it takes a year or more for new roads to show up, but it'll happen eventually. So there's a chance that defunct businesses will be removed and new ones added. That's not the case with the TOPO maps.
Or, for free, you can look into Open Street Map maps, some of which include topography, and because of the way they're created and maintained, are more likely to be rapidly updated. The OSM maps for my area include all of the local trails, while my TOPO maps have very few. I have OSM maps on my Epix for just this reason, and flip to them whenever I'm out hiking or cross country skiing.
