I've used both a good bit. Avare is free and Naviator has a 30 day free trial, so you can't go wrong with just trying both of them out. Here's some quick thoughts on both of them.
Avare:
Free
No geo-referenced approach plates
Geo-referenced airport diagrams
No vector maps
Clunky interface (just my opinion)
Fast redraw speed
Good support from the developer
Naviator:
Interface has gotten much better over time, but still not great
Good support for various external hardware units, including ADS-B
Synthetic Vision in the latest release
Slow redraws (have not tested this in latest release, may not be an issue)
Good Support from the developer