I have Foreflight and WingX currently downloaded for the trial. It seems WingX does give you a little bit more for your money in the base version (terrain and synthetic vision without going pro), but I think I like the interface a little better on Foreflight. But I need to play with it some more. I just have been planning mock trips.
Make sure you try them out in an airplane. What works and looks nice in your La-Z-Boy in the den may not be the best choice in a bumpy airplane with less than optimum screen visibility.
Also don't forget about watching the WingX videos on YouTube. They will show you how to get the most out of WingX.
I downloaded the trial version of ForeFlight a while back and was very disappointed at what was not there. The following come in the base version of WingX that I did not see in the trial version of ForeFlight.
Terrain data base
Obstacle and terrain warning
Simulator for runniing through your flight plan
Split screen
Georeferenced airport diagrams
Synthetic vision (99 cents)
Descent glideslope calculation
Flight recorder (Rewind) that records all GPS and AHRS parameters during flight
Extended runways overlay showing landing pattern
A very handy intutive distance calculator on map screen
In route terrain altitude / above ground level display toggle
Terrain summary that can be selected to show a graph of the flight route or the next 50 miles from your current GPS position.
Winds aloft altitude selector to help you pick the optimum altitude for your flight
WingX can use a multitude of ADS-B and AHRS boxes, FF only works with Stratus.
There are probably other differences I don't remember. If I have mis-stated anything above, please correct me. This is not intended to be for or against either program but rather a factual list of the differences in the base version.
It would be really neat if there were a features comparison matrix to factually show the differences between WingX, FF and Garmin Pilot and to point out what comes in the base versions of each program versus what the 'Pro' version of each adds.