In my region, google maps has worked pretty well. It rarely gets mentioned though...is it not cool? Their offline capabilities have come a long way, so I used it without a data plan for almost 2 years. I would just pre-load the map before leaving. So "no signal" was really "no problem". Eventually, they even built directions into the offline capability. These days I have data, so it works even better (data when I have it, and offline when I don't). For where I am, the data is quite accurate and the fidelity is good. Even the smallest access roads I have been on where accurately depicted and titled. I have tried a few others, and of course some of my friends run other software as well, but I haven't yet seen something that seemed to be better in terms of quality or features.
I will add though, that I try to encourage my friends to know the area we are in through some research before we go (regardless of what software or device is used in-vehicle). Sometimes our group is so dependent on the "directions" provided in the device that if there is any hiccup the group gets befuddled. For example, not knowing the major east-west and north-south roads that surround your area. That is not good. I also carry a high quality paper map as well, but I will admit that until paper can learn to zoom in and out at varying levels of detail, it is hard to beat the digital devices.