Avare is nice and free, but I find the UI hard to use. I'd rather pay for an app that has a better UI.
SkyVector is free and has Canadian charts, but is a bloated piece of crash-ware on every device I have owned over the years. I love their web site, hate their Android app.
Naviator and Droid EFB (formerly Avilution) are my 2 favorite apps and I maintain current subscriptions with both. In comparison:
Both:
Seamlessly stitched charts
Easy route building, by entering waypoints or touching on-screen.
Connect over BT to external GPS
Connect over GDL-90 WiFi to ADS-B receivers (like Stratux and others)
Falls back to internal GPS, if it exists
Create flight tracks and save/upload to their servers
Regular updates and responsive support
Droid EFB:
Faster, smoother response (you can tell the difference even on fast tablets)
Longer battery life (app is less of a battery hog)
Smooth zoom: can zoom the map to any level large or small (not step-zoom)
Automatically synchronizes waypoints and routes across all devices
Shows PIREPS (Naviator doesn't)
Shows wind (Naviator doesn't)
Better night mode
Better display of ADS-B "in" traffic
Shows fuel prices
Built-in Weight & Balance app
Has exact printed copy of AF/D and airport diagrams
Naviator:
Better graphics & chart detail (vector graphics: sharper when zoomed in close)
Step-zoom only: zoom only to predefined steps, so sometimes you can't get the zoom you want because it's between levels
Terrain DB with colored warning areas on charts (Droid EFB only highlights obstacles, not terrain)
Better online web "Hangar" listing & displaying your flights
Terrain, airports, and navaids (VORs, NDBs) cover Canada -- but not charts
Altitude optimizer (but only during pre-flight (internet connection), not during flight (ADS-B in weather), since Naviator doesn't process wind from ADS-B in).
Cheaper annual subscription
Overall Droid EFB is my primary app, mainly because of longer battery life in-flight, better handling of ADS-B "in" traffic, and syncing all your waypoints & routes across all your devices and they never get deleted even if you completely uninstall the app. But Naviator is a good app and I like having a completely separate app (and device) as a backup.