I agree it's a matter of preference and needs.
I always want a navigation app that is mostly off-line since my monthly data budget is only 200MB. There's still a lot within that category and you'll see a lot of threads on it. I've tried Osmand, Mapfactor, Locus Pro, Navfree, Mapdroyd. I spent quite awhile comparing and finally settled on Navfree about a year ago and haven't looked back.
Here are my personal rankings/reviews for (mostly) off-line navigation apps:
======#1 Navfree======
* Advantage: Simple settings interface (almost to a fault, not a lot of options).
* Advantage: Simple navigation screen with voice prompts. Easy to see the turns.
* Advantage: Easily use google to quickly get a location. Specifically: can turn on data, use the built-in google search (within the app) for an address or a business name (mcdonalds), set that location as favorite or destination, then turn data back off (don't need it for navigation). Also of course you can use your normal voice input with the built-in google search if your keyboard supports it. This gives a very handy way to quickly access locations without spending much data.
* Advantage: Street/address location without data. Although I find can be a little tricky. I use the option above (data on for built-in google search) more often.
* Advantage: Ability to show a lot of detail at a given zoom. When I compare a given zoom to the other apps listed, Navfree has more streets listed. And the street labels are as big or bigger on Navfree. And with all this somehow surprisingly Navfree is not more cluttered(!). It's just better organized to fit the street labels in there, and leave off non-essential info.
* Advantage: You can tap on a street (when not navigating) to see it's name. Such a simple feature... but absolutely necessary and none of the other apps have it. On the other apps when scrolling around you'll sometimes have to scroll and zoom just to identify the name of a particular street that is shown but not labeled on your display.
* Advantage: above two advantages make it easier (compared to other apps) to get an overview of a route/area by scrolling around and zooming in/out. I have compared this aspect among apps because I consider it important that the app must allow me to familiarize myself with an area/route by scrolling around. Navfree is better than the others at this.
* Disadvantage: Not a lot of options (it can be an advantage, over time you just get used to the way they set things up).
* Disadvantage: The only display mode when navigating is that the top of the screen is the direction you're heading (there is no north=up mode while navigating)... AND there is no compass on the display while navigating. So when navigating there is nothing on the screen you can use to give you any clue whether you're headed N, S, E, W! This was very annoying to me at first, but I have become proficient at a "work-around": If I want to orient myself with respect to compass direction while navigating, I scroll a bit which temporarily exits navigation and pops up a compass in LLHC, then I view the compass or tap it to reorient the map as "north=up". Then when I have seen enough to get my sense of direction, I hit the navigate button to resume navigation (returns to forward=up with no compass)
* Advantage: there is traffic feature on the paid version. Of course it needs data. Works ok for me because I only occasionally need traffic. I start my trip without data/traffic and only turn data on data/traffic when I sense I am headed for a conjested area. It fills in the traffic colors without having to exit navigation mode.
* Big Disadvantage: The favorite-location feature doesn't allow editing of entries (except by deleting/reentering), doesn't allow reordering of entries, and doesn't allow nesting of entries within folders/categories. That's very crude compared to all the others. In another thread someone suggested using contacts to store addresses, but that is a little too cumbersome to me, and sometimes Navfree can't decipher the address stored in the contact. My coping strategy is to simply keep the number of my Navfee favorite locations in the range 10-20 so I can easily find things in the list (more than 20 and it's very tough to find anything because they're not categorized and not well ordered (can't reorder). To keep the number of favorites low (10-20), that means I have to delete things, like deleting favorites for a city that I don't plan on visiting again soon. If I go back to the same city a few months later, I have to set up the favorite locations again. That's not ideal, but I find it tolerable because it is relatively easy re-establish most favorites before the trip or in hotel (on wifi) using the in-built google-search mentioned above. That reminds me....
* advantage: local google search from a specified location which is not necessarily where you are currently located. A handy feature for planning your trip ahead of time.
* advantage: if you stray from your route it automatically reroutes
* disadvantage: on occasion the route it suggests is clearly non-optimal. So I find it reasonable to zoom out and check the route before I take it. If I prefer another route, I can't force it to that route (there are no waypoint feature). So I just drive my own route and eventually it automatically reroutes to match my route.
* disadvantage: you can't share a location from another app into Navfree... it never appears in the share menu.
* Advantage: The app makes me successful in following directions without a lot of effort and without making mental mistakes. While I don't like not having a north-up option, the forward-up orientation makes life simpler for recognizing the road pattern on the screen and matching it to the road pattern in front of the windshield at complicated intersections. The navigation route is highlighted in a bold purple color which is easy to see but doesn't overwrite the street names. There are extra red turn arrows to identify exact location of the turns. Turns are of course also displayed at top of screen and announced when coming up and when it's time to make the turn. It zooms in and out according to my actual speed such that my apparent "speed" on the screen is almost always (*) the same... specifically it takes about 30 sec to travel from bottom of screen to the thing that was on top of the screen, regardless of speed. (* The exception is near a turn when it zooms in a little more.). The color scheme, arrows, pan-rate etc represent a lot of attention to small details in the display which make it easier to see the essential info at a glance. The others don't do these small things as well imo.
Each time I try one of the others, it doesn't last long before I go back to Navfree. I guess I'd have to admit I have adapted my style to work around some of the shortcomings of Navfree. I have a hard time separating whether my opinion about the program is from the fact that I have used it for so long. For whatever the reason, for me it is now a clear #1, far better than the others in my eyes.
=====#2 - MapFactor =====
Compared to Navfree, this has many of the same features and much better favorite management (can edit and organize favorites into nested folders), also a few more choices of view when driving like north up. And it shows up on the share menu when sharing location from another app. But I really didn't like that the background of the search bar was dark blue and the text in it was black, so I couldn't see what had been entered (by voice or soft keyboard) in the search box. This illustrates the opposite of Navfree in terms of attention to small detail of display colors and sizes to make things easier to see at a glance. It also doesn't have the great level of detail for road labeling like Navfree nor the touch-a-street to get the road name.
====#3 - Osmand =====
Very customizeable. But at the time I reviewed it, the settings/configuration was mind-numbingly complicated. They lost track of KISS somewhere along the way. And it stalls if you ask it to navigate a long trip. I also find I am more likely to miss a turn using Osmand at a complicated intersection because the instructions and visual cues are not as immediately clear. It's not quite tuned in / dialed in for seeing things at a glance the way Navfree is.
====# 4- Locus Pro=====
Seems like very general map program where navigation was only an afterthought. Lots of complicated features for waypoints, tracking, kml etc. Just not very good at simple car navigation.
====#5 - MapDroyd.====
Too basic / Not enough features. I saw it recently on someone's list of top-5 or top-10 offline apps and I don't think it competes with most of the others.